Question

A mixture consists of two radioactive materials A₁ and A₂
with half lives of 20 s and 10 s respectively. Initially the
mixture has 40 g of A₁ and 160 g of A₂. The amount of the
two in the mixture will become equal after
(a) 60 s (b) 80 s
(c) 20 s (d) 40 s