Here are two winter mornings. In one town the thermometer reads −7 °C. In another town it reads −3 °C.

Hands up: which town is colder? And here is the tricky part — which number is actually the greater number, −7 or −3?

The number line shows two markers at a time. Watch where each one sits: the number further to the left is always the smaller one. See if you can call the greater number before it's confirmed.

Now we work through five pairs together on the board, deciding the greater number in each one. For every pair we drag marker A from one end of the line to the first number and marker B from the other end to the second, and read which one sits further right — that one is the greater number. First predict, then place, then check as a class.

Now we work through five more together on the board, placing the greater number of each pair: the greater of −3 and −8, then the greater of +1 and −5, then the greater of −7 and −2, then the greater of 0 and −9, and finally the greater of −4 and −6. Predict where the answer lands before each marker goes down.