math
posted by alex .
A material has a halflife of 12 hours. If initially there are 4 grams of the material, how much is present after 8 hours?
I know the answer is 8/3, but how would you solve this using calculus? please help.

no need for calculus.
the amount left after t hours is
4 (1/2)^(t/12)
when t=8, that is
4 (1/2)^(2/3)
= 2.52
I think the 8/3 = 2.67 answer is bogus. Close, but nowhere near exact. 8 is 2/3 of 12, but that's not how halflives work.