Question

The half-life of a radium isotope is 1,600 years. after 4,800 years, approximately how much of an original 10.0kg sample of this isotope will remain

Answer 1

1/2 * 10 = 5 kg is left after 1600 years

after 2 more periods of 1600 years  amount left = 5 * 1/2 * 1/2  =  5/4 kgs

Answer:-    after 4800 years there is 1.25 kgs left