# algebra

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The half-life of plutonium-234 is 9 hours. If 40 milligrams is present now, how much will be present in 4 days? (Round your answer to three decimal places.)

• algebra -

after h hours,

40 * (1/2)^(h/9)

That's because for every 9 hours, the amount is multiplied by 1/2

so, after 4 days = 96 hours, we will have

40 * (1/2)^(96/9) = .0246 mg

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