Fractions and decimals

Swapping between the two forms.

Know the common ones

A half is 0.5 and 50 percent, a quarter is 0.25, a fifth is 0.2, an eighth is 0.125 and a third is about 0.333. Recognising these on sight removes most fraction arithmetic.

To add fractions, put them over the same bottom number first.
To divide by a fraction, multiply by it upside down.

Fractions as division

Three quarters of 60 is 60 divided by 4 times 3, which is 45. Doing the division first keeps the numbers small.