If you need to find a percentage of a number, here's what you do – for example, to find 35% of 240: Divide the number by 10 to find 10%. In this case, 10% is 24. Multiply this number by how many tens are in the percentage you're looking for – in this case, that's 3, so you work out 30% to be 24 x 3 = 72.