Substance X has a half-life of 45 years and decays into substance Y. A meteorite sample contains 2% of X and 14% of Y by quantity. Assuming Y was absent initially and all Y came from X, what is the approximate age of the meteorite?

270 years
135 years
90 years
45 years

Correct answer: 135 years

Solution

Initial X = 2 + 14 = 16 units. Remaining X = 2 units. Fraction = 2/16 = 1/8 = (1/2)³. Number of half-lives = 3. Age = 3 * 45 = 135 years.

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