Question

Radium has a half-life of 1,620 years. In how many years will a 1 kg sample of radium decay and reduce to 0.125 kg of radium?

Answer 1

4680 years

1 x .5 = .5

.5 x .5 = .25

.25 x .5 = .125

You multiplied 3 times, so 3 times 1,620 is 4,680.