Thursday

July 2, 2015

July 2, 2015

Number of results: 48,831

**AP Environmental Science (URGENT)**

Strontium-90 is a radioactive waste product from nuclear reactors. It has a half-life of 29 years. How many years will it take for a quantity of strontium-90 to decay to 1/16 (one-sixteenth) of its original mass?
*January 11, 2012 by Heather*

**Math**

Suppose strontium-90 decays at a rate of 2 percent per year. (a) Write the fraction P of strontium remaining, as function of t, measured in years. (Assume that at time t=0 there is 100 % remaining.) Answer: P(t) = (b) Estimate the half-life of strontium. Answer: Hint: Use your...
*June 27, 2014 by Anonymous*

**calculus**

Suppose strontium-90 decays at a rate of 2 percent per year. (a) Write the fraction P of strontium remaining, as function of t, measured in years. (Assume that at time t=0 there is 100 % remaining.) Answer: P(t) = (b) Estimate the half-life of strontium. Answer: Hint: Use your...
*June 27, 2014 by Anonymous*

**NEED HELP WITH CALC**

Suppose strontium-90 decays at a rate of 2 percent per year. (a) Write the fraction P of strontium remaining, as function of t, measured in years. (Assume that at time t=0 there is 100 % remaining.) Answer: P(t) = (b) Estimate the half-life of strontium. Answer: Hint: Use your...
*June 27, 2014 by Anonymous*

**Calculas**

In the early 1960s, radioactive strontium-90 was released during atmospheric testing of nuclear weapons and got into the bones of people alive at the time. If the half-life of strontium-90 is 32 years, what fraction of the strontium-90 absorbed in 1965 remained in people's ...
*August 26, 2010 by Cratch*

**calculus**

In the early 1960s, radioactive strontium-90 was released during atmospheric testing of nuclear weapons and got into the bones of people alive at the time. If the half-life of strontium-90 is 27 years, what fraction of the strontium-90 absorbed in 1962 remained in people's ...
*July 3, 2012 by jessica*

**Chemistry**

The half-life for beta decay of strontium-90 is 28.8 years. A milk sample is found to contain 10.3 ppm strontium-90. How many years would pass before the strontium-90 concentration would drop to 1.0 ppm?
*November 11, 2011 by Mindy*

**chemistry**

Strontium-90 decays through the emission of beta particles. It has a half-life of 29 years. How long does it take for 80% of a sample of strontium-90 to decay? Show process of how you got this
*January 10, 2013 by Urgent Help*

**Chemistry**

Strontium-85, used for bone scans, has a half-life of 64 {\rm d}.How long will it take for the radiation level of strontium-85 to drop to \frac{1}{8} of its original level?
*April 27, 2011 by Help!!*

**Math**

The half-life of strontium-90 is 28 years. How long will it take a 60 mg sample to decay to a mass of 15 mg?
*May 19, 2010 by Caitlyn*

**chem**

Radioactive substances decay by first-order kinetics. How many years would be required for a sample containing strontium-90 to decrease to 58.32% of its initial activity? The half-life of strontium-90 is 2.88e1 years.
*February 22, 2014 by sara*

**chemistry**

Strontium-90 has half-life of 28 years. if a 1.00-mg sample was stored for 112 years. what mass of Sr-90 would remain?
*April 6, 2010 by bob*

**Calculus**

The half-life of radioactive strontium-90 is approximately 31 years. In 1960, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 11 percent of the original is...
*February 17, 2014 by Brandon*

**SCIENCE**

We did a radioactive decay and half life lab with m&ms and I do not understand these conclusion questions: 1. how many half lives would it take for 500 nuclei to decay to 6.25% of the original number of nuclei? My ans: 3125?- do not think that's right! 2. Is there any way to ...
*November 27, 2014 by Bethany*

**Calculus**

The half-life of radioactive strontium-90 is approximately 31 years. In 1960, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 11 percent of the original ...
*January 13, 2011 by Brittany*

**Math**

The half-life of radioactive strontium-90 is approximately 28 years. In 1962, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 6 percent of the original ...
*August 28, 2012 by Jason*

**Math**

The half-life of radioactive strontium-90 is approximately 32 years. In 1961, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 8 percent of the original ...
*September 19, 2012 by Annie*

**Science**

Can anyone help me find the half-life of strontium-90? I also need an explanation on how to do it. Thanks!! Radioactive Decay of Strontium-90: At 0 years: 100% remaining At 28 years: 50% remaining At 56 years: 25% remaining At 84 years: 10% remaining At 112 years: 5% remaining.
*March 12, 2015 by Jane*

**Calculus**

[Exponential growth & decay] The half-life of radioactive strontium-90 is approximately 29 years. In 1965, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only ...
*October 6, 2009 by Z32*

**Chemistry**

Will you check this answer for me? the half-life of strontium-87 is 2.8hr. What percentage of this isotope will remain after 8 hours and 24 minutes? ?? 34%
*May 25, 2011 by Madison*

**math**

a life insurance agent is to be paid a commission according to the following scheme : 1000$ in year 1, half the year 1 amount in year 2, half the year 2 amount in year 3, etc. what is the total of the all amounts received by the agent in the first 5 years ?
*April 19, 2013 by Anonymous*

**physics**

If the physical half-life of sulfur-35 is 87.1 days, and the biologic half-life in the testicle is 632 days, what is its effective half-life in this organ? I know i have to find the time and then the half-life. But im having trouble finding the time A(t)=Ao x e ^ (-0.693) (t...
*October 24, 2013 by Sarah*

**Chemistry**

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years? A. 2.0 grams of 198 Au B. 2.0 grams of 42 K C. 4.0 grams of 32 P D. 4.0 grams of 60 Co By the way the numbers next to the elements are their atomic masses. thanks ...
*March 3, 2007 by Sanjay*

**physics**

A building has become accidentally contaminated with radioactivity. THe longest lived material in the building is strontium-90 (atomic mass of 90 Sr 38 is 89.9077). If the building initially contained 5.0kg of this subtstance and the safe level is less than 10.0 counts/min, ...
*February 16, 2007 by soojung*

**Calculus**

If 40 milligrams of strontium-90 radioactively decays to 12 milligrams in 30 years, find its half-life (the number of years it takes until half of it remains). Use the formula A = p ⋅ e−kt, where p is the amount and A the (smaller) final amount.
*March 26, 2014 by Kimberly*

**chemistry**

If there are 80 milligrams of a radioactive element decays to 10 milligrams in 30 minutes then what is the elements half life in minutes? Ok i narrowed it down to either 10 or 30...but im rly confused so if u could help it wuld be grea 80 40 1 min 20 2 min 10 3min looks like ...
*March 4, 2007 by jojo*

**chemistry**

When 3.761g of a hydrate of strontium chloride is heated to 60 degree C it forms strontium chloride dihydrate of mass 2.746g What is the formula of the original sample?
*June 8, 2011 by aryan*

**science**

1. What is the half-life of Strontium-90? Explain your answer. Honestly I don't know how to get this answer. I've looked it up and stuff, but I just found the answer not how to know what it is. A link or explanation would be greatly appreciated. Thanks.
*February 27, 2014 by Rainshine*

**calculus**

The rate at which an amount of a radioactive substance decays is modeled by the differential equation dA/dt = kA, where A is the mass in grams, t is the time in years, and k is a constant. Answer the following. a) If a 100-gram sample of the radioactive substance decays to 95 ...
*March 19, 2012 by ronnieday*

**Chemistry**

Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half life of 2.48 * 10^5 years Thorium-230 has half life of 8.0 * 10^4 years Radium-226 has half life of 1.62 * 10^3 years Lead-210 has half life of 20.4 years. The rate constant for the decay of unstable nuclide X...
*March 20, 2012 by Harry*

**science**

what is the Half-life of strontium 90. Explain your work. Okay well I already know the answer is 28yrs but I just don't know how to explain it on how I got the answer... can you guys help me please! I need this done in 30 seconds..
*January 8, 2015 by Channy-Boo*

**chemistry**

Find the number of disintegrations per minute emitted by 1.1 mol of 232-Th in 1 min. The half-life of 232-Th is 1.4 x 1010 year I was able to do this with the following technique: 1.1 x 6.022 x10^23 =6.62x10^23 1.4x10^10=7.358x10^15 minutes I think then it is 6.62x10^23 x 7....
*August 2, 2012 by Nancy *

**Nuclear Physics**

An investigator receives Co-60 (5.27 year half life) for use in a research study. Unfortunately the Co-60 is contaminated with Cs-137 (30.0 year half life). The initial Co-60 activity is 400 times the initial Cs-137 activity. How long after the initial assay will the Cs-137 ...
*February 3, 2011 by amy*

**Chemistry**

Mefenamic acid (Ponstan Forte) has a half life of 2 hours. Naproxen has a half life of 12 to 17 hours. Both are anti inflammatory drugs of apparently similar nature but could someone please explain the difference in half life? Thank you Mike
*August 13, 2009 by Mike*

**Algebra**

The half-life of a specific radioactive compound is 20 years. The equation used to model this half-life is y = 5 1/2(t/20) where t represents time. Currently, there are 5 pounds of this compound 15 feet below the earth's surface. When will there only be 4 pounds of this ...
*December 18, 2014 by Zyere *

**chemistry**

strontium chloride can be obtained as the anhydrous salt, SrCl2, and as the hydrates SrCl2.2H20, and SrCl2.6H20. (ArSr = 87.5). 0.323 g of a sample of strontium chloride is dissolved in water and reacted with sliver nitrate solution. The mass of sliver chloride precipitates is...
*March 17, 2007 by kate*

**physics**

If a radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the 2nd year?
*August 23, 2012 by Anonymous*

**Science**

if a radioactive isotope has a half-life of one year, how much of the original sample will be left at the end of the second year?
*August 23, 2012 by aileen*

**Science**

if a radioactive isotope has a half-life of one year, how much of the original sample will be left at the end of the second year?
*August 23, 2012 by aileen*

**life science**

I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
*February 7, 2008 by claire*

**Science**

If a loaded truck that can accelerate at 1 m/s2 loses its load and has one-half of the original mass, what acceleration can it attain from the same driving force?
*May 20, 2014 by Justin Wyms*

**chemistry**

What percent of the original sample of strontium-90 (half-life = 28.9 years) will remain after the following time periods?after 18 years? after 47.5 years? after 1008 years?
*November 5, 2011 by Anonymous*

**half-life**

ok so i got... the half life of carbon-14 is 5730 years, the relation c+(1/2)^ N/5730 is used to calc. the concentration, c, in parts per trillion remaining n years after death determine the carbon concentration in a 11460 year old bone. please help :)
*June 30, 2010 by bubb*

**half-life**

ok so i got... the half life of carbon-14 is 5730 years, the relation c+(1/2)^ N/5730 is used to calc. the concentration, c, in parts per trillion remaining n years after death determine the carbon concentration in a 11460 year old bone. please help :)
*June 30, 2010 by bubb*

**half life**

tritium has a half life of 24.3 years .a sample of 0.1 is produced . will tthe mass of tritium change after 24.3 years
*April 14, 2011 by Anonymous*

**half-life**

1. The half-life of a first-order reaction is 9.89 minutes. How many minutes will have elapsed after 27 half-lives? My answer is 267.03. 2. The half-life of a second-order reaction is 2.508 days. How many days will have elapsed after 8 half-lives? My answer is 5.330. Is this ...
*February 7, 2007 by Issac*

**linear/exponential**

This question involves the half-life formula. In this exercise, we are to give a half-life for an exponentially decaying quantity. Need answer to the following: The half-life of a drug in the bloodstream is 4 hours. By what factor does the concentration of the drug decrease in...
*November 24, 2007 by kayse*

**Physics HELP HELP**

(for some reason I keep getting this wrong. I put 90 for c, 5.6 for h and 22 for M(x), Then I took the natural log of both sides, but I keep getting it wrong) The mass of a radioactive element at time x is given by the equation below, where c is the original mass and h is the ...
*November 10, 2010 by Anonymous*

**chemistry**

Strontium has density of 2.64 and crystallizes with the face-centered cubic unit cell. Find the radius of the strontium atom
*July 10, 2011 by hannah*

**Chemistry**

Strontium metal is responsible for the red color in fireworks. Fireworks manufacturers use strontium carbonate, which can be produced by combining strontium metal, graphite (C), and oxygen gas. The formation of one mole of SrCO3 releases 1.220 x 103 kJ of energy. a) Write a ...
*December 3, 2012 by Veronica*

**Chemistry**

The half life of U238 is 4.5 x 10^9 yr. A sample of rock of 1.6 g produces 29 dis/sec. Assuming all radioactivity is due to U238 find percent by mass of U 238. I have tried ln(t)/ln(0)= -kt and still cannot get the answer What I get is A) 4.5x10^9 x365x60x60x24=1.419x10^17 for...
*September 22, 2013 by Nancy *

**Earth Science**

Why is potassium-argon dating most applicable to dating very old rocks? potassium’s long half-life potassium’s short half-life argon’s long half-life argon’s short half-life
*February 21, 2013 by Anonymous*

**chem**

If the passing of three half-lives leaves 33.1 mg of a strontium-90 sample, how much was present in the beginning?
*October 6, 2014 by Mg Good*

**Science**

A star's life depends on mass ___ mass=Long life Large mass= ____ life Small mass is long life and large mass is short life?
*August 28, 2014 by Coleson*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*September 18, 2013 by Nadia*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*September 19, 2013 by Nadia*

**Chemistry **

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hr and is a pure gamma emitter. Suppose that 200mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals? 1- One half ...
*September 19, 2013 by Nadia*

**college**

. S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
*May 3, 2010 by kurt*

**chemistry**

The radius of a strontium atom is 215 pm. How many strontium atoms would have to be laid side by side to span a distance of 4.47 mm?
*September 8, 2014 by Anonymous*

**college chem**

S-35 (t1/2 = 87.4 d) is used in cancer research. The biological half-life in the human body is 90 days. What is the effective half-life of S-35?
*May 3, 2010 by Anonymous*

**chemistry**

A given reaction has an activation energy of 24.52 kJ/mol. At 25C the half-life is 4 minutes. At what temperature will the half-life be reduced to 20 seconds?
*April 9, 2011 by Eddy*

**Math**

The mathematician Augustus DeMorgan lived his entire life during the 1800s. In the last year of his life he announced "Once I was x years old in the year x^2". In which year was he born?
*October 2, 2012 by Sadie*

**chemistry**

1-Barium sulfate and strontium sulfide both are placed into beaker of water. a- Will the strontium sulfide dissociate? ....... - If it does,write the equation showing the dissociation.
*May 5, 2012 by Marie*

**college chemistry**

If the equilibrium constant (Keq) equals 9.12x1012 for the following reaction between strontium and magnesium: Sr(s) + Mg2+(aq)<==> Sr2+(aq) + Mg(s) Calculate Eo for a strontium=magnesium battery.
*April 13, 2011 by alex*

**college chemistry**

If the equilibrium constant (Keq) equals 9.12x1012 for the following reaction between strontium and magnesium: Sr(s) + Mg2+(aq)<==> Sr2+(aq) + Mg(s) Calculate Eo for a strontium=magnesium battery.
*April 13, 2011 by alex*

**chemistry**

If I 131 has a half-life of 8 days, what fraction will be left after a year?
*July 7, 2011 by g*

**help huge test friday science**

I cant grasp half life - the study guide question is how is half life dating used by scientists - I have 2 lines to write an answer
*February 8, 2008 by claire*

**Math **

Suppose a quantity is halvd every 18 years. use the approximate half-life formula to estimate its decay rate. is the half life equation y= 1/2^t1/2 2^1/2t= 1/y t 1/2= log2 (1/y) Where do I put 18 at?
*December 4, 2009 by Randi*

**chemistry**

what is the percentage yield for Sr(NO3)2 + Na2SO4 -> SrSO4 + 2 NaNO3. mass of strontium nitrate is 0.788g mass of sodium sulfate is 1.258g mass of dry filter paper 0.759 g mass of dried precipitate in filter paper 1.317g
*December 19, 2013 by Dianna*

**AP Chem**

I know this might sound easy... but i need these problems for bonus and i want to make sure they are right Silver nitrate reacts with strontium chloride in an aqueous precipitation reaction. What are the formulas of silver nitrate and strontium chloride? Write the molecular ...
*October 27, 2008 by Anna-Marie*

**Math - D.E.Q.**

The half-life of a radioactive isotope is the amount of time it takes for a quantity of radioactive material to decay to one-half of its original amount. i) The half-life of Carbon 14 (C-14) is 5230 years. Determine the decay-rate parameter for C − 14.
*January 18, 2011 by Justin*

**Physical Science**

A gram of radioactive material has a half-life of one year. After four years how much radioactive material will be left...0g, 1/2g, or 1/4g? None of the above. The answer one-half to the fourth power.
*March 29, 2007 by Gina*

**math**

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physics. You purify a sample of 2 grams. One of your colleagues steals half of it, and eight days later you find that 0.1 gram of the radioactive material is ...
*October 21, 2012 by Roseanne*

**Calculus **

Radius decays at a rate of that is proportional to its mass, and has a half-life of 1590 years. If 20 g of radium is present initially, how long will it take for 90% of this mass to decay?
*June 17, 2010 by Anonymous*

**chemistry**

what ins the name for SrBr2 Strontium (II) bromide strontium bromide
*November 16, 2006 by queen*

**math**

Suppose your bank account was worth $1000 at the beginning of last year. If your balance increased by 3% during the first half of the year and by 2% during the second half, what was your balance at the end of the year?
*February 10, 2014 by Anonymous*

**Atomic physics**

1)Five possible transitions for a hydrogen atom are listed below: Select whether the atom gains or loses energy for each transition. a. Loses Gains ni = 6; nf = 4 Loses Gains ni = 4; nf = 2 Loses Gains ni = 5; nf = 3 Loses Gains ni = 2; nf = 5 Loses Gains ni = 5; nf = 7 b. ...
*April 13, 2008 by Sandhya*

**Half-life**

After two hours, 1/16 of the initial amount of a radioactive isotope remains undecayed. What is the half-life of the isotope?
*November 18, 2013 by Andrea*

**algebra**

Suppose a sample of Cesium-137 with initial mass of 200 grams decays to a mass of 160 grams voer the course of 10 years. Find the half-life of Cesium-137 (Round to the nearest year) How much Cesium-137 is left in the sample after 60 years? Round to the nearest tenth of a gram.
*July 30, 2011 by Melanie*

**Physics - Half life**

an artifact has a starting mass of C-14 of 200 g and a remaining mass of 0.78125 g. how old if the artifact? [4.58^4 years]
*June 25, 2012 by Anonymous*

**calculus**

The half-life of Radium-223 is 11.43 days. If a sample has a mass of 900 mg, find the mass (in mg) that remains after 5 days
*October 14, 2010 by Connor*

**calculus**

The half-life of Radium-223 is 11.43 days. If a sample has a mass of 400 mg, find the mass (in mg) that remains after 6 days
*October 14, 2014 by w*

**Math**

In 1976 a research hospital bought half a gram of radium for cancer research. Assuming the hospital is still exists, how much of this radium will the hospital have in the year 6836 if the half-life of radium is 1620 years?
*July 31, 2011 by Kate*

**Math**

In 1976 a research hospital bought half a gram of radium for cancer research. Assuming the hospital is still exists, how much of this radium will the hospital have in the year 6836 if the half-life of radium is 1620 years?
*August 1, 2011 by Kate*

**chemistry**

How do you find the half-life of an element? Please explain and show me how to do this. I know the answer is 14.3 days, but I don't know how to work it. thank you! the problem is: After 42 days, a 2.0-g sample of phosphous-32 contains only 0.25g of isotope. What is the half-...
*December 13, 2007 by Ryan*

**Half-Life**

Uranium-238 decays to Lead-206. The half life of Uranium-238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes?
*February 19, 2012 by Noah*

**Finance**

An insurance company says you can pay for your life insurance by paying $100 at the beginning of each year or $51.50 at the beginning of each half-year. They say the rate of interest underlying this calculation is j2=3%. What is the true value of j2? The answer in the textbook...
*October 5, 2014 by Mella*

**Gen Chem**

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239-Np to decay to 1.00% of its original quantity? I got: close to 15 days. Is this right? I figured that about 1% of the original quantity would be roughly 6.5 Half lives, and since a half ...
*March 28, 2008 by Sarah H*

**math**

Daniel's print shop purchased a ner printer for $35000. Each year it depreciates (loses value) at a rate of 5%. what will its approximate value be at the end of the fourth year?
*June 14, 2009 by Anonymous*

**Chem Class**

The rate constant of a first-order process that has a half-life of 225 s is ?????? s-1. ok so i divided half life of 1st order= 0.693/K k i put 225 and i got 3.08 x 10^-3 is that right?
*October 25, 2010 by Laynie*

**Geology**

If the decay constant for radioactive decay of ^40 K is λ = 5.543*10^(-10) / year, use this equation to calculate ages of the samples in the following table: t(1/2) = 0.693/λ 1)What is the half life of 40K? table -----Np --- Nd---- Nd/Np A)6439-----2303---0.358 B)...
*November 21, 2013 by Maura*

**Radioactivity or science**

A radioactive isotope source has a mass of 120ug. If the isotope had a half life of 20s, what would be the mass if the isotope after 2 mins?
*April 21, 2014 by Jannet*

**Radioactivity **

How are the terms "activity" and "becquerel" related? A radioactive isotope source has a mass of 120 g. If the isotope has a half life of 20 secs what would be the mass of the isotope in 2 mins?
*April 16, 2014 by Anonymous *

**Chemistry**

Half-life N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
*December 1, 2012 by Paul*

**Math/Radioactive Dating**

How would I calculate the age of a rock only given the amount of each in grams and half-life? 40K decays to 40Ar. Half life of 40K is 1.25 billion years. 40K = 20 grams 40Ar= 5 grams I think the formula is Final Amount of 40K = Initial Amount of 40K * (1/2)^(time/half-life) If...
*February 19, 2011 by Lena*

**physics**

The moon is receding from the Earth by approximately 3.8 cm per year. Earth's mass is 5.98 x 10^24 kg, and its radius is 6.38 x 10^6 m. The Moon's mass is 7.3 x 10^22 kg, its radius is 1.79 x 10^6 m, and its orbital period around Earth is 27.3 days. The current average ...
*December 16, 2008 by Michelle*

**Math**

The average life expectancy for American men born in 1900 was 55 years. Life expectancy has increased by about .2 year for each birth year after 1900. If this trend continues, for which birth year will the average life expectancy be 85 years? how do u write and equation for to...
*November 6, 2008 by i love polka*

**Science Half Lives**

I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7)
*January 25, 2011 by Krys*

**Chemistry**

K-42 has a half-life of 12.4 hours. If you begin with 250g of K-42, determine how much you will have left after 4 half-lives. How long does 4 half-lives take? please help
*May 15, 2011 by Jazmin *

**physical science**

Determine the molar mass of the following elements: a. manganese, Mn c. arsenic, As b. cadmium, Cd d. strontium, Sr
*December 4, 2008 by Jameisha*