SOLUTION: The half-life of strontium-90 is 28 years. How long will it take a 72 mg sample to decay to a mass of 18 mg? Your answer is years.

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Question 416076: The half-life of strontium-90 is 28 years. How long will it take a 72 mg sample to decay to a mass of 18 mg?
Your answer is years.
Answer by richard1234(7193) About Me  (Show Source):
You can put this solution on YOUR website!
For this problem, there is no need to use logarithms since it decays from 72 mg to 18 mg (one-fourth of the original amount). Hence, exactly two half-lives are required, so it would take 56 years.