# The half-life of iodine-131 is 7.2 days. How long will it take for a sample of this substance to decay to 30% of its original amount?

##### 1 Answer

Dec 11, 2017

**To decay** **of original amount it will take** **days.**

#### Explanation:

Half life of iodine -131 is

We know

Taking natural log on both sides we get,

When

To decay