A 400g sample Iodine-131 has a half-life of 8 days. How much will be left after 40 days?

Hey there!

A half-life means after a certain amount of time, half of that substance will be gone/changed after that time.

There are 5 half lives in 40 days because 40 ÷ 8 = 5.

So, we divide the 400g sample in half 5 times.

400 ÷ 2 = 200

200 ÷ 2 = 100

100 ÷ 2 = 50

50 ÷ 2 = 25

There will be 25g of iodine-131 remaining after 40 days.

Hope this helps!