How to Do Basic Percentages with the Table of Joy
Working out the sum, which is normally the easy bit.
Shade in the grid like a chessboard, so the squares alternate between dark and light, with the shaded squares making an ‘X’.
Find the two numbers that are in the same coloured squares and write them down with a x between them (in this case, 340 x 20).
After this, write down a divide sign and the remaining number. For this example, the Table of Joy sum is 340 x 20 ÷ 100.
Do the sum 340 x 20 = 6,800; divide this by 100 to get 68 – which means £68 is 20% of £340.