# A radioactive isotope has a half-life of 9 hours. How do you find the amount of the isotope left from a 80-milligram sample after 54 hours?

##### 1 Answer

Dec 30, 2015

After 54 hours, 1.25 milligrams of the sample will be left.

#### Explanation:

After a half-life period, the quantity of the sample with be reduced to half.

So, after 9 hours, amount of sample left

After another 9 hours, amount of sample left

or,

Do you see the pattern emerging?

In 54 hours, there are

Therefore, amount of sample left after 54 hours

= amount of sample left after 6 half-life periods