You tin rate notice swap the per centum as well as the amount: 16% of £25 is hard to calculate inwards your head, just 25% of £16 is exactly the same amount.
So if you lot desire to speedily function out 16% of £25 without a calculator, honour 25% of £16 instead (ie split £16 past times 4). Simple!
Think most why this works.
Source: www.aperiodical.com
