Another look at multiplying by zero and one, and the relationship between multiplication and division.

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.

More work on doubling and halving, including larger numbers and fractions.

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).