A/A0
= 6/30 and time interval t = 10 days
If A/A0
= ½ (=1/21) then t = 1 half-life
If A/A0 = ¼ (=1/22) then t = 2 half-lives
If A/A0 = 1/8 (=1/23) then t = 3 half-lives
Therefore if A/A0 = 1/2N then t = N half-lives
6/30 = 1/2N
1/5 = 1/2N
5 = 2N
Taking logs we get:
log10
5 = log10 2 x N
therefore N = 2.32
This means that 10 days =
2.32 half-lives, therefore one half-life is 4.3 days
Try this out on the excel
worksheet