Improve your Mental Maths

Strategies

Here are some to try out:

To divide by 2, just halve
To divide by 4, halve twice
To multiply by 2, double
To multiply by 4, double twice
To multiple or divide by 10, move the digits along
To divide by five, double the number and divide it by 10
When adding, start with the tens, not the units
Use near doubles, like 6+5 is the same as double 6, take away 1
When adding, find the easy pairs. Example: 12+7+8 is easier as 12+8=20, then add 7
Count up to do some subtraction. Example: 103-97 is done by counting on from 97 to 103

Do you know any more? Why not add them to this thread?