Maggie was doing research for her Ph. D. in physics when a 12 mg sample of radioactive material decayed to 3 mg in 26 minutes. Determine the half life of this substance.

The general way to work this out is to solve the general expression for

the remaining quantity versus half-life, using logarithms. But that's not

necessary with these numbers.

Look at the numbers:

- - 3 mg is 1/4 of 12 mg.

- - 1/4 is the product of (1/2) x (1/2).

- - So the 3 mg is what's left of 12 mg after 2 half-lives.

The 26 minutes must be two half-lives.

- - The half-life of that substance is 26/2 = 13 minutes.

Go Maggie!