SAT Subject Physics Practice Question 621: Answer and Explanation

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Question: 621

2. The half-life of a radioisotope is one week. How much of the substance is left after a 28-day period?

A. 1/2
B. 1/4
C. 1/8
D. 1/16
E. 1/32

Correct Answer: D


The correct answer is (D). During a period of 28 days, the sample has 4 half-lives. This means (1/2)4 = .0625, or 1/16 of the substance is left.

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