# Pre Calculus

posted by Brianna

If a 25 mg sample of radioactive material decays to 18.4 mg in 5 years, how long will it take the sample to decay to 20.5 mg?

1. Steve

25*e^-5k = 18.4
So, k = ln(18.4/25)/-5 = 0.0613

So, now just solve for t in

25*e^-.0613t = 20.5

2. Anonymous

bcx xb

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