Addition

When adding columns such as:

25
34
98

First add up the numbers the numbers in the left column that are multiples of 10 – they’re easy. So 20+30+90=140.

Then add up the numbers in the right coloumn – 5+4+8=17.
Simply add the two totals together, and you’re there! 140+17=157.

What's a really simple way of adding 9 or 90? For example: 78 + 9 =?

Easy - first you add 10 to make 88, and then take one away to make 87.

Adding ten, then taking one away is the same as adding nine - but it's much quicker!

The same rule works with adding 90. For example: 86 + 90 =?

Easy again - first you add 100 to make 186, and then take ten away to make 176. Adding 100 then taking 10 away is the same as adding 90.