The Table of Joy is a handy tool for working out percentages, ratios, conversions and much else besides! Here’s an example how you can use it to convert 300 miles into kilometres, using the fact that 5 miles is roughly 8 kilometres:

Draw out a big noughts and crosses style grid.

Leave the top-left square blank and label the rest of the top row with the things you’re converting: in this case, miles and kilometres.

Again, leaving the top-left square blank, label the rest of the leftmost column with the information you have: the conversion

*rate*and the*distance*you’re converting.Put the numbers you know in the logical places: 5 in the rate/miles square, 8 in the rate/kilometres square and 300 in the distance/miles square.

Now shade the grid like a chessboard. Multiply the two numbers in the same-coloured spaces, and divide by the other. Here, it’s 300 x 8 ÷ 5 = 480km.