Posted by alejandro on Tuesday, July 3, 2012 at 4:16am.
The mass of a radioactive sample is represented in the graph below. The initial mass of 32 mg decays to 8 mg after 21 hours.
1)What is the half-life of the radioactive sample, in minutes?
2)Solve each equation.
a. 4 8x-1 = 8
b. 3^(2x-5) = 1/27x
math30 - Steve, Tuesday, July 3, 2012 at 5:17am
8 is 1/4 of 32, so two half-lives = 21 hours.
half-life is 10.5 hours
4^(8x-1) = (2^2)^(8x-1) = 2^(16x-2) = 8 = 2^3
so, 16x-2 = 3
x = 5/16
assuming 1/27x = (1/27)*x,
3^(2x-5) = (3^-3)x
(2x-5)log3 = -3log3 + logx
(2x-2)log3 = logx
assuming a typo, and the x on the right does not belong,
3^(2x-5) = 1/27 = 3^-3, so
2x-5 = -3
x = 1
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