Answer:
To calculate half life, divide original value by 2.
1.
FOUR HALF LIVES = divide original value by 2, 4 times.
40÷ 2 = 20
20 ÷ 2 = 10
10 ÷ 2 = 5
5 ÷ 2 = 2.5g
2. AFTER TEN DAYS (TWO HALF LIVES)
140 ÷ 2 = 70
70÷ 2 = 35g
AFTER TWENTY DAYS (FOUR HALF LIVES)
140 ÷ 2 = 70
70 ÷ 2 = 35
35 ÷ 2 = 17.5
17.5 ÷ 2 = 8.75g
