Doubling 2-digit numbers and halving 3-digit numbers mentally.

Some people like to start doubling with the units, others like to start with the tens. It doesn?t matter as long as the method is fast and accurate.

When we are multiplying by a number ending in 5 we can double the number and halve the other number before multiplying (by a multiple of ten, making it easy).

Some people (especially those who still use feet and inches!!) think it is important to know how to multiply by 12. It?s easy ? just add 10 times the number to 2 times the number.