# How do you find the half life of uranium-235? I tried to do 235 / 2 = 117.5 but that is wrong please help

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half life is when you half/divide a number by 2 does this necessary mean that you divide or do you have to work out something else before dividing?

half life is when you half/divide a number by 2 does this necessary mean that you divide or do you have to work out something else before dividing?

##### 1 Answer

Please see the explanation.

#### Explanation:

To find the half-life of any radioactive substance, you need to start with an initial mass of the substance,

The decay of radio active substances follow this equation:

Both

Let's solve for

Please notice that

Now suppose that you are given a value for

We know that the left side is

Suppose that you are given the half-life and you need to find

The half-life for

For