The half-life of a radioactive kind of strontium is 3 hours. If you start with 64 grams of it, how

much will be left after 9 hours?

8

Explanation:

If strontium has a half-life of 3 hours and you have 64 grams of it that means every 3 hours strontium's grams will be divided by 2.

So you have 64/2 = 32 for the first half life {Time is currently at 3 hours}

32/2 = 16 for the second half life {Time is currently 6 hours}

Then you have 16/2 = 8 for the third half-life {Time is currently 9 hours}