Question

If a radioisotope has a half life of 10 years, how much of the original material would remain after 40 years?

Answer 1

Instead of dividing the material by half each time, start by dividing 40 years by the half life of ten. This gives you 4. Subtract 1 So you the answer is 1/2 to the 3rd power

Answer 2

1/8 would remain...
(1/2 is 10 years
1/4 is 20 years
1/8 is 40 years)

Hope this helps! :)