Question

isotope A require 12h for its decay rate to fall to 1/64 of its intial value . isotope B has half-life = 1.5 half life of A
how long does it take for decay rate of B fall to 1/32 of its initial value ?

Answer 1

(1/2)^ 6 = 1/64

so we are talking six half lives for A is 12 hours
so one half life for A is 2 hours

Now I will read the problem :)

well half life of B is 3 hours

1/32 = 5 half lives

5 * 3 = 15 hours

Not hard, just keep your wits about you and think ! (and check my arithmetic :)