Bismuth-214 has a half life of about 20 minutes. Find the amount of Bismuth-214 left from a 30-gram sample after 1 hour
Each 20 minutes there is 1/2 as much one hour is 3 half lives :
start 30 then 15 then 7.5 then 3.75 gm
30(1/2)3 = 3.75 gm
+36916 
