How much of a radioactive kind of tin will be left after 30 days if you start with 160 grams and the half-life is 10 days?
After 10 days you will have 160/2 = 80 grams left.
After another 10 days you will have 80/2 = 40 grams left.
After another 10 days (30 in all) you will have 40/2 = 20 grams left.
3010=3 half-lives
160 x 2^-3=20 grams left after 30 days.
