# How can near doubles help me add numbers?

Are you good at doubling numbers? This can help you add numbers that are close to each other.

The trick is to double a number that you know and then add on or take away the difference.

If you know that **10 + 10 = 20** then this can help you work out **10 + 11**.

**10 + 11** is the same as **10 + 10 + 1** which makes **21**.

## Example

**9 + 12 = ?**

**9** and **12** are both close to **10**.

**10 + 10 = 20**

**9** is **1** less than **10**, so take this away.

**20 – 1 = 19**

That leaves the **12**. It is **2** more than **10** so you need to add this on.

**19 + 2 = 21**

You’ve just worked out that **9 + 12 = 21**.