Posted by **alex** on Sunday, November 11, 2012 at 11:41pm.

A material has a half-life 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.

- math -
**Steve**, Monday, November 12, 2012 at 12:18am
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 half-lives work.

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