Quote Originally Posted by tice1212
Test c has a half live of 12 days so on day 13 it should be all out
That answer is wrong on two fronts.
You are wrong on the half life and you are wrong on how half lives work.

Test C has a half life of approximately 8 days.

Also, after one half life only half of the compound is gone.
Day 0 - 100%
Day 8 - 50%
Day 16 - 25%
Day 24 - 12.5%
Day 32 - 6.25%
Etc...