# What are the formulas for half-life in exponential decay?

##### 1 Answer

Sep 15, 2014

The formulas for half-life are

The equation for exponential decay is

**(1)**

We can solve this for

**(2)**

And the formulas for half-life

**(3)**

and

**(4)**

If you know the value of

**EXAMPLE**

Technetium-99m is used for brain scans. If a laboratory receives a shipment of

200 g of this isotope and only 12.5 g of this isotope remain after 24 h, what is the half-life of technetium-99m?

**Solution**