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

nope

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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