Question

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half of its initial mass. Starting with 195 g of radioactive isotope how much will be left after five lives? round to the nearest gram

Answer 1

1st half life: 195/2 = 97.5 g
2nd half life: 97.5/2 = 48.75 g
3rd half life: 48.7/2 = 24.375 g
4th half life: 24.375/2 = 12.1875 g
5th half life: 12.1875/2 = 6.09375 g

or you can do
195(2)^(-5) = 6.09375
** rounded to nearest gram = 6 g