posted by TITA .
If a sample of a radioactive isotope has a half-life of 5 year(s), how much of the original sample will be left at the end of the second year?
How much will be left at the end of the third year of thr original sample?
How much will be left at the end of the fourth year of the original sample?
Fraction left at t = (1/2)^(t/T)
where T is the half life, which is 5 years in this case.
For the first question, solve
(1/2)^(2/5) = 75.8%
Repeat using the same formula for the other times t.