# Radioactive element X has a half-life of 30 days. A rock sample contains 4 grams element X when it forms. How many half-lives will have elapsed in 90 days? How much of the original amount of X will be unchanged after 90 days?

##### 1 Answer

Jul 19, 2018

#### Explanation:

Given that radioactive element X has a half-life

Hence the number

The amount

hence the amount left after