Multiplying by 101 or 99 in your head. Sounds difficult, but you can do it by multiplying by 100 and then adjusting.

Multiplying whole numbers and tenths by a single digit. When multiplying numbers like these it is a good idea to start with the whole number or units.

Multiply a decimal fraction by 10 or 100: remember to move the digits one place to the left or two places to the left.

Finding common multiples of pairs of numbers.