# 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 not sure what I missed.

A 2.5 gram sample of a radioactive element was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of the radioactive element is 28 years. How much of this element will remain after 112 years?

I tried it this way 112/28= 4 half lives then 2.5/3 1.25
1.25/2=0.625
06.25/2= 0.3125
0.3125/2=0.15625 gram

which is the correct way to do these problems. Am I doing that the correct way

1. 👍
2. 👎
3. 👁
1. 1. 30 years= 3 1/2 lives so
1.0mg ->30yrs-> 0.5mg
0.5mg->30yrs->0.25mg
0.25mg->30yrs->0.125mg

2. correct

1. 👍
2. 👎

## Similar Questions

1. ### chemistry

For the following reaction KClO2->KCl+O2 assign oxidation states to each element on each side of the equation. Reactants K=? Cl=? O=? Which element is reduced? I got K=5, Cl=-1, and O=-4 . The element that reduced is K, but its

2. ### Chem help

Answer the questions below for an element that has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s1. A. What is the symbol for this element? B. What is the atomic number of this element? C. How many unpaired electrons does an

3. ### 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.

4. ### 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

1. ### 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 =

2. ### Chemisrty

Answer the questions below for an element that has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s1. A. What is the symbol for this element? B. What is the atomic number of this element? C. How many unpaired electrons does an

3. ### 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

4. ### Physics

The electronic configuration of an element X is: 1s² 2s² 2p6 3s2 3p5 Deduce the atomic number of X To what group does it belong Give two properties of the group to which the element X belong. Identify element X by name. Write a

1. ### chemistry

elements below, indicate how each elements’ valence electrons act in a chemical reaction. Insert an L if an element loses electrons, a G if the element gains electrons, an E if the element can either lose or gain electrons, and

2. ### 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),

3. ### 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

4. ### 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