# The half-life of calcium-47 about 5 days. Starting with 64 g of this isotope, what would be the amount remaining after 20 days?

##### 1 Answer

Aug 3, 2016

The answer is 4 g.

#### Explanation:

Divide 64 by 2 four times, because there are four half-lives in 20 days.

Every half-life, the calcium-47 will lose half of the amount remaining.