Question

The half-life of radium is 1690 years. If 30 grams are present now, how much will be present in 720 years?

Answer 1

22.3 gm

Explanation:

720 is this many half lives : 720 / 1690

so there will be this much left 30 gm ( 1/2)^(720/1690) = 22.3 gm