Elevenses

In his grid, how many pairs of numbers can you find that add up to a multiple of 11?
Do you notice anything interesting?

Can you see a connection with the 11-hour clock?
Can you find all the pairs?
Could you convince someone that you haven’t missed any?

Can you use the same ideas to find all the pairs of numbers that add up to multiples of 13? This time there are not as many pairs.

Click here for the Notes for Teachers