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A reactant A decays through two parallel first-order paths, A -> B and A -> C, with individual half-lives of 60 min and 90 min respectively. What is the overall half-life of A?

1. 36 min
2. 45 min
3. 54 min
4. 72 min

Correct answer: 36 min

Solution

1/t = 1/60 + 1/90 = 1/36, giving overall half-life 36 min.

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