If 12g of radioactive substance are present initially and 7 years later only 6g remain, how much of the substance will be present after 11 years?

Question

After 11 years there will be how many g’s of radioactive substance?

Round 3 decimal places

Answer 1

First, find the half-life.  Then use the half-life to find the amount at 11 years.

 

T = half-life

 

6 = 12(0.5)^7/T

 

Solve for T and get T = 7 years.

 

A(t) = 12 (0.5)^t/7

 

A(11) = 12 (0.5)^11/7 ≅ 4.038 g