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Problem 4 - Entrance Test

A radioactive sample has a half-life of T. What fraction of the original sample remains after a time of 3T?

Correct: A

After one half-life (T), 1/2 remains. After two half-lives (2T), 1/2 * 1/2 = 1/4 remains. After three half-lives (3T), 1/2 * 1/2 * 1/2 = 1/8 remains.