Two different radioactive isotopes decay to 10% of their respective original amounts. Isotope A does this in 33 days, while isotope B does this in 43 days. What is the approximate difference in the half-lives of the isotopes?

Reaching 10% of the original amount takes the same number of half-lives for each isotope: about 3.32, since (1/2)^3.32 ≈ 0.10. The difference in their times to reach 10% is 43 − 33 = 10 days, so the difference in half-lives is about 10 ÷ 3.32 ≈ 3 days. The correct choice is A, 3 days.

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