A radioactive element has a half-life of 8 days. If you start with 640 grams, how much remains after 32 days?
Answer
40 grams
How to solve it
1
32 days = 4 half-lives (32 ÷ 8)
2
After 8 days: 640 ÷ 2 = 320 g
3
After 16 days: 320 ÷ 2 = 160 g
4
After 24 days: 160 ÷ 2 = 80 g
5
After 32 days: 80 ÷ 2 = 40 g
Hints
Calculate number of half-lives
Divide by 2 for each half-life