The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 135grams of a radioactive isotope, how much will be left after
4half-lives?

Question

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 135grams of a radioactive isotope, how much will be left after 
4half-lives?

dumbcow · Answer

1/2 is left after 1 half life
1/2*1/2 = 1/4 is left after 2 half lives
...
(1/2)^n  is left after "n" half lives

anonymous · Answer

thank you so much! what is the answer in grams? You were very helpful @dumbcow

dumbcow · Answer

take the fraction and multiply it by original amount... 135

--->135*(1/2)^4

anonymous · Answer

8 grams?