SOLUTION: The half-life of strontium-90 is 28 years. How long will it take a 44 mg sample to decay to a mass of 11 mg?

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Question 156528: The half-life of strontium-90 is 28 years. How long will it take a 44 mg sample to decay to a mass of 11 mg?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Half life means you at that time you have 1/2 of what you started with.
Today you start with 44 mg.
In 28 years, you will have (1/2)(44)=22 mg left.
After another 28 years, you will have (1/2)(22)=11 mg left.
Total time to 11 mg = 56 years.