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At a given instant, say t = 0, two radioactive substances A and B have equal activities. The ratio B A R R of their activities after time t itself decays with time t as e –3t . If the half-life of A is l n2, the half-life of B is -

1. ln 2 4
2. 4 l n2
3. 2 l n2
4. ln 2 2

Correct answer: ln 2 4

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