the number of grams of radioisotope that have remained after 12 days if the half life if 4 days is calculated as below
calculate the number of half lives involved
12/4 = 3 half live are involved
40 after one half life = 40/2 = 20 g
20g after the second half life = 20/2 = 10g
10g after the third half life = 10/2 = 5 g
therefore 5 g will be remaining
