To find out how much you need when you need a fraction of a number like 1/3 of 9, you can multiply the whole number by the fraction in most cases.
In some cases however, you can convert the whole number into a fraction and then divide it to get the amount in fractional units that you require.
For example:
1/3 of 9
Convert 9 to a fraction.
1/3 / 9/1
1/3 x 9/1 = 3/9
Therefore you would need 3 of 9 for 1/3.
