# IF 80mg of a radioactive element decays to 10mg in 30 minutes, the half-life of this element is a.10 min b.20 min c.30 min d.40 min the answer is a.10 min but i would like to know why, please help.

26,448 results

Which of the following statements about radioactive dating is true? a. Radioactive decay is the rate at which new atoms form. b. During radioactive decay, atoms break down, releasing particles or energy. c. The rate of decay of a radioactive element cannot

2. ## Calculus-Modeling Equations

An unknown radioactive element decays into non-radioactive substances. In 420 days the radioactivity of a sample decreases by 39 percent. 1.What is the half-life of the element? 2.How long will it take for a sample of 100 mg to decay to 46 mg?

3. ## Science

Radioactive substance decays so that after t years, the amount remaining, expressed as a percent of the original amount, is A(t)=100(1.6)^(-t). a) Determine the function A’, which represent the rate of decay of the substance. b) what is the half-life for

4. ## PRe calc story problem!!

A radioactive element decays exponentially according to the function Q(t) = Q0ekt .If 100 mg of the element decays to 25 mg in 12 days, find the half-life of the element.

5. ## Calculus

A certain radioactive material decays exponetially. The percent, P, of the material left after t years is given by P(t)= 100(1.2)^-t a)Determine the half life of the substance

6. ## Chemistry

Gallium65, a radioactive isotope of gallium, decays by first order-kinetics. The half-life of this isotope is 15.2 min. How long would it take for 7/8 of a sample of this isotope to decay? 15.2 min 30.4 min 45.6 min 48.0 min I'm not sure how to do this. I

7. ## College algerba

The​ half-life of a certain radioactive element is about 1500 years. After 2800 ​years, what percentage P of a sample of this element​ remains?

8. ## Chemistry

As a sample of the radioactive isotope 131 I decays, its half-life a)decreases b)increases c)remains the same

9. ## Math

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay

10. ## math

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element? half-life: b)How long will it take for a sample of 100 mg to decay to 51

11. ## Calculus

A certain radioactive material is known to decay at a rate proportional to the amount present. A block of this material originally having a mass of 100 grams is observed after 20 years to have a mass of only 80 grams. Find the half-life of this radioactive

12. ## Calculus

The rate of decay is proportional to the mass for radioactive material. For a certain radioactive isotope, this rate of decay is given by the differential equation dm/dt = -.022m, where m is the mass of the isotope in mg and t is the time in years. A. If

13. ## Physics

100g of radioactive element X are placed in a sealed box. The half-life of this isotope of X is 2 days. After 4 days have passed, what is the mass of element X in the box? b) If the box is completely evacuated (perfect vacuum), then N atoms of X are added.

14. ## Chemistry

IF 80mg of a radioactive element decays to 10mg in 30 minutes, the half-life of this element is a.10 min b.20 min c.30 min d.40 min the answer is a.10 min but i would like to know why, please help.

15. ## math

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

16. ## college algebra

if 60% of a radioactive element remains radioactive after 300 million years, then what percent remains radioactive after 500 million years? what is the half-life of this element?

17. ## Physic

A radioactive element x has half life of 30 days and will decay to become another new element Y.. a) calculate decay constant b) how long it will take for 90% of the no.Of atom in radioisotope x to decay?

18. ## college algebra

In 4 years, 30% of a radioactive element decays. Find its half-life. (Round your answer to one decimal place.) _____ yr

19. ## Math

Household smoke detectors contain 200μg of a radioactive element that has a half-life of 432 years. To the nearest 10μg, how much of this element will remain after 20 years? a) 190 μg b) 100 μg c) 200 μg d) 180 μg

20. ## 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

21. ## 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

22. ## pre calc

A radioactive element decays exponentially according to the function Q(t) = Q0ekt .If 100 mg of the element decays to 25 mg in 12 days, find the half-life of the element. please help

23. ## chemistry

What is the half-life of an isotope if it decays to 12.5% of its radioactivity in 18 minutes?

24. ## pre calculus

if 17 percent of a radioactive substance decays in 12 hours, what is the half-life of the substance? Round your answer to one decimal place.

25. ## Chemistry

A radioactive sample contains 3.25 1018 atoms of a nuclide that decays at a rate of 3.4 1013 disintegrations per 26 min. (a) What percentage of the nuclide will have decayed after 159 d? % (b) How many atoms of the nuclide will remain in the sample? atoms

26. ## Algebra 2

A particular radioactive element has a half life of 10.0 days. How much is left after 30.0 days if the sample started with 345g?

27. ## Pre calc

If 250 mg of a radioactive element decays to 200 mg in 48 hours, find the half-life of the element

28. ## 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

1. For the 1st order reaction whose rate law constant, k, is 1.5x10-3s-1, t½ is a. 7.7 minutes *** b. 462 minutes c. 6.5 minutes d. 4.5 minutes 2. If the half-life of a 1st order reaction is 137 minutes, k= a. 8.43x10-5s-1 b. 11,900 s-1 c. 5.06x10-3s-1

30. ## Math

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay

31. ## math with application

If 12 % of a radioactive substance decays in 7 hours, what is the half-life of the substance? Carry out all calculations exactly, then round the final answer to three decimal places. The half life is what hours?

32. ## Chemistry

A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 h. What is the half-life of this radioactive isotope?

33. ## Alg2

Radioactive iodine is used to determine the health of the thyroid gland. It decays according to the equation y=ae -0.0856t where t is in days. Find the half-life of this substance. Round to the tenths place.

34. ## chemistry

A radioactive sample contains 3.25 1018 atoms of a nuclide that decays at a rate of 3.4 1013 disintegrations per 26 min. (a) What percentage of the nuclide will have decayed after 159 d? % (b) How many atoms of the nuclide will remain in the sample? atoms

35. ## 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.

36. ## Pre Cal

a radio actice substance decays so that half of the substance decays every 2 minutes. if 100 g of the substance are present initially, how many grams will be present after 4 minutes and 8 minutes respectively?

37. ## Calculuc

How do you set up this problem? The decay constant for the radioactive element cesium 137 is .023 when time is measured in years. Find its half-life.

38. ## Calculus

Write a differential equation to model the situation given. Do not solve. The radioactive substance neptunium-139 decays to 73.36% of its orginal amount after 24 hours. How long would it take for 43% of the original neptunium to be present? What is the

39. ## 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

40. ## Engineering Math

An unknown radioactive element decays into non-radioactive substances. In 120 days the radioactivity of a sample decreases by 59 percent. What is the half life of the element? How long will it take for a sample of 100 mg to decay to 77 mg? The answer is

41. ## half-life

If 250mg of a radioactive element decays to 200mg in 48 hours, find the half-life of the element. ln(No/N) = kt No=250 mg N = 200 mg t = 48 hours. Solve for k, then put k into the following equation and solve for t1/2. k = 0.693/t1/2

42. ## math30

The mass of a radioactive sample is represented in the graph below. The initial mass of 32 mg decays to 8 mg after 21 hours. 1)What is the half-life of the radioactive sample, in minutes? 2)Solve each equation. a. 4 8x-1 = 8 b. 3^(2x-5) = 1/27x

43. ## Science

Choose the explanation that does the following: (1) identifies the element used in carbon dating and (2) explains why the element is used. A. iodine-131; iodine is present in the thyroid glands, is radioactive, and has a very long half-life B. nitrogen-14;

44. ## Science

An element has a half-life of 29 hours. If 100 mg of the element decays over a period of 58 hours, how many mg of the element will remain? So far I have; n= elapsed time/ half-life =58/29 n=2

45. ## Science

Natural Uranium contains 15 percent Sm147. Sm147 is radioactive and decays by alpha decay. What will be the number of disintegrations per gram per second of the natural element? The half-life of Sm147 is 1.3x1010 years.

46. ## Math

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physic. You purify a sample of 2 grams.One of you colleges steals half of it, and 3 days later you find that 0.1 grams of the radioactive

47. ## 8th Grade Earth Science Help?

Which of the following terms refers to the time it takes for one-half of the radioactive atoms in a sample of a radioactive element to decay? - relative age - absolute age - potassium-argon data - half-life** Is my answer correct?

48. ## Chemistry

A certain radioactive element has a half life of 1 h. If you start with a 1-g sample of the element at noon, how much is left at 3:00 PM? At 6:00PM? At 10:00 PM?

49. ## College algebra

If 70% of a radioactive element remains radioactive after 400 million years , then what percent remains radioactive after 600 million years? What is the half-life of this element

50. ## physics

Calculate the half-life of a radioactive substance that decays by a factor of 3 in concentration every 1 million years

51. ## Pre Calculus

Exponential Growth and Decay Find the half-life of a radioactive substance that decays by 5% in 9 years.

52. ## 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

53. ## Chemistry

All isotopes of technetium are radioactive, but they have widely varying half-lives. If an 800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639,000 y, what is its half life

Radioactive decay is the process by which an unstable element transforms into different element, typically releasing energy as it does so. For 500g of a radioactive substance with a half-life of 5.2 hours, the amount remaining is given by the formula

55. ## Alg2

Radioactive iodine is used to determine the health of the thyroid gland. It decays according to the equation y=ae -0.0856t where t is in days. Find the half-life of this substance. Round to the tenths place.

56. ## Chemistry

The radioactive nuclide 18F decays by first order kinetics with a half life of 1.83 hr. How many hours will it take for 68.5% of a give quantity of 18F to decay?

57. ## Algebra 2

A radioactive substance decays at a rate of y = ae^-0.1483t, where t in in hours. Find the half-life of the substance. How do I solve this problem if I am only given the constant.

58. ## science

If the half life- period of a radioactive element is 1600.After how many years will if remains 25% of his quantity

59. ## Physic

A radioactive element x has half life of 30 days and will decay to become another new element Y.. a) calculate decay constant b) how long it will take for 90% of the no.Of atom in radioisotope x to decay?

60. ## physics

Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the half-life is 22 hrs? What is the initial activity of the sample in decays per minute?

61. ## Precal

If 80 percent of radioactive element is left after 250 years, then what percent remains after 600 years? What is the half life of the element?

62. ## Math/Calculus

After 5 days, a particular radioactive substance decays to 37% of its original amount. Find the half life of this substance. Is this right? Th= ln 2/ln(1/.37) x 5 days

63. ## Chemistry

A radioactive element has a half-life of 6.41 days. What percent of the original sample will be left after 15.0 days?

64. ## Physcis 30

Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)? How many will remain after two half-lives (60 seconds)? Three half-lives? So basically, after 30 seconds it will

65. ## Chemistry

2. The half-life of a radioactive element is important when considering its application in medicine. For example, iodine-131 is often used in the imaging of the thyroid. The reason is that iodine is readily absorbed by the thyroid gland. Another reason is

66. ## 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.

67. ## chemistry

a radioactive material is undergoing nuclear decay. After 40 minutes, 25% of the sample remains. What is the half-life of the sample

68. ## Precalc

Element X is a radioactive isotope such that every 86 years, its mass decreases by half. Given that the initial mass of a sample of Element X is 730 grams, how much of the element would remain after 9 years, to the nearest whole number?

69. ## Chemistry

If a radioactive isotope has a half life of 162 days how many half lives would it need to go through to have 50% of that isotope to be non-radioactive?

70. ## abdul kabir

the half life of an element is 5 days. if we have 10gram of the element initially. what is the mass of the element after 5days and 10days

71. ## Science

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

72. ## chemistry

Some radioactive nuclides have very short half-lives, for example, I-31 has a half-life of approximately 8 days. Pu-234, by comparison has a half-life of 24,000 years. Explain why both of these examples are dangerous, even though their half-lives are very

73. ## Chemistry

If 30% of a sample of radioactive isotope decays in 24 hrs, what is the half-life? How do i know which order to use? and do I convert hr to mins or seconds? Pls help for my exam tomorrrow

74. ## Algebra

A radioactive kind of nitrogen has a half life of 10 minutes. If you start with 64 grams of the substance, how much will be left after 20 minutes?

75. ## Physics

A radioactive substance decays from 2.0kg to 1.6kg in 156 days. What is the decay constant and the half life of the substance?

76. ## Chemistry

If a half life of a radioactive element is twelve years,find the decay constant

77. ## Physic

A radioactive element x has half life of 30 days and will decay to become another new element Y.. a) calculate decay constant b) how long it will take for 90% of the no.Of atom in radioisotope x to decay?

78. ## physics

Radon 86222Rn is a radioactive gas with a half-life of 3.82 d. If there are initially 400 decays/s in a sample, how many radon nuclei are left after 2 d ? Please help, I don't understand how to do this.

79. ## Pre Calculus

Exponential growth and decay find the half life of a radioactive substance if 220 grams of the substance decays to 200 grams in 4 years?

80. ## physics

Radioactive nuclei are produced in an irradiated sample at the rate of 10 s-1. If the number in the sample builds up to a maximum of 1000, calculate the mean life and the half-life of the radioactive nuclei Using dN / dt = P - λ N dN / dt = 1000n /10/ 1 =

81. ## chemistry

A particular radioactive substance has a half-life of 4 minutes. How long will it take for 250 g of this radioactive material to decay to less than 0.1g? 24 min 36 min 40 min 48 min 72 min I got 32 min but that not one of the choices. Please help

82. ## math

I asked the following the other day and received the following answer: Posted by Matthew on Sunday, March 17, 2013 at 11:03pm. A quantity of oxygen gas had 16.32 g of the radioactive isotope oxygen-19 in it. When measured exactly 10 minutes later, the

83. ## Chemistry

A particular radioactive element has a half life of 10.0 days. How much is left after 30.0 days if the sample started with 345g?

84. ## College algebra

The radioactive element has a half-life of about 28 years and sometimes contaminates the soil. After 47 years, what percentage of a sample of the elements remain?

85. ## Algebra

In 10 years, 25% of a radioactive substance decays. What is its half-life? A. 25 years B. 24 years C. 20 years D. 29 years

86. ## Science

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value?

87. ## algebra 2

element x has a half life of 90 seconds. How much of a 100 gram sample of element x is left after half an hour

88. ## Science

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value? Can anyone give me a VERY SIMPLE explanation of this please? Thank you.

89. ## Chemistry

Tc-99 is a radioactive isotope that decays by beta emission and is used by radiologists in the diagnosis of liver disease. Its decay behavior is shown by the activity-time table. What is its half-life?

90. ## Chemistry Numerical

The half life period of a radioactive element is 27.96 days. Calculate the time taken by a given sample to reduce to 1/8th of its initial activity

91. ## Science

What happens to the mass of a sample containing a radioactive element during its half-life? A. The mass decreases by half. B. The amount of mass is doubled. C. Eventually there is no mass at all. D. The mass remains the same.

92. ## Physics

A radioactive source has a half-life of 6 days.How long will it take for the count rate to fall from 180 per minutes to 145.

93. ## math

What is the figure that gives the half-life of the isotope in minutes to 4 significant figures? Exponential regression on a set of data, which gives the amount of atoms of a radioactive isotope remaining after a time X minutes, produced the following

94. ## Pre-calc

At the beginning of an experiment, a scientist has 296 grams of radioactive goo. After 120 minutes, her sample has decayed to 9.25 grams. What is the half life of goo in minutes?

95. ## statistics

I have tried for days to figure out how to work this problem. Please help show me how to find the answer. A particular radioactive isotope decays from 210 mg to 182.7 mg in 15 days. Find the half life of the isotope.

96. ## Ordinary differential equations

A radioactive isotope sits unused in the lab for 10 years at which it decays to 80% of original amount. Find the half life and the addition years it takes to reduce to 15%of original amount

97. ## chemistry

Radioactive waste is difficult to dispose of due to the long time periods needed before the radiation effectively disappears. The US protocol is to store the waste for 10 half-lives of the material after which the waste is no longer considered radioactive.

98. ## Chemistry

A radioactive substance has a half-life of 3 minutes. After 9 minutes, the count rate was observed to be 200. What was the count rate at zero time?

99. ## Math

In 10 years, 25% of a radioactive substance decays. What is its half-life? A. 25 years B. 24 years C. 20 years D. 29 years

100. ## Chemistry

The most abundant isotope of the element nobellum has a half-life of 58 minutes. After 174 minutes the sample has a mass of .300 mg. What was the orignal mass of the sample? A. 1.20 mg B. 4.80 mg C. .600mg D. 2.40 mg