# algebra

The level of thorium in a sample decreases by a factor of one-half every 4.2 million years. A meteorite is discovered to have only 7.6% of its original thorium remaining. How old is the meteorite?

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1. Let N be the number of half-lives in its age
(1/2)^N = 0.076

Solve for N and multiply N by 4.2 million years.

N = log 0.076 / log 0.5 = 3.72

Age = 15.6 million years

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posted by drwls

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