# Once a certain medicine is in the bloodstream, its half-life is 21 hours. How long will it be before an initial 30cc of the medicine has been reduced to 7cc?

##### 1 Answer

Nov 18, 2016

Here is the formula given by my teacher to solve this problem.

#### Explanation:

A represents the initial amount, in this case, it is 30cc

B is the base, half-life is always 1/2

And t represents time, we are told that it half every 21 hours, hence it should be

The answer is round to two decimal places.