A centimetre is a unit used to measure the length of things, like a pencil can be 12 centimetres (or 12cm) long. 1cm is equal to 10 millimetres (or 10mm) and you need 100cm to make 1 metre (1m).

Chunking is a good way to do your division sums, where you take off big chunks of the number you're dividing by, instead of taking off the number one by one, which would be really boring. So for 54 ÷ 3, first take off 30 (3 x 10), then take off 15 (3 x 5), then the final 9 (3 x 3), which means you have taken off 18 lots of 3 in total (10 lots + 5 lots + 3 lots). So, 54 ÷ 3 = 18.

The column method is a good way to do your addition sums, where you add up the biggest digits first, then the next biggest, and so on, and you write them out in a neat column underneath. Why? Because it makes adding them up afterwards a lot easier.

A coordinate is a way of saying where something is, for example, on a map. All coordinates are written to show how far away they are from the starting point (0,0). They tell you how far along it is, then how far up it is (some say 'along the corridor and up the stairs).

Counting on is a good way of working out your subtraction sums, where you start from the smaller number (which you are taking away) and count up in jumps to the bigger number (which you started with). Add the jumps together and, hey presto!, there is your answer, the difference between the two numbers.