Copyright © University of Cambridge. All rights reserved.

I have a pile of nine digit cards numbered $1$ to $9$.

I take one of the cards. It is the $3$.

Which card would you choose to go with the 3 so you could make the largest possible two-digit even number with the two cards?

We put the cards back in the pile. This time, I choose the $6$. Which card would you choose this time to go with the 6 to make the largest possible two-digit even number?

Have a go at this with a partner. One of you chooses the first digit from the set of cards. The second person then chooses a card to make the largest possible two-digit even number. You can then swap over.

Try it several times so you are sure you have a good method. Talk about your ideas with your partner so you agree together on a 'best' method.

How would your strategy change if you had to make the largest two-digit odd number?

If you don't have a partner to work with, you could use the interactivity below. The computer selects one digit at random. You must then choose a digit to make the largest possible two-digit even number or largest possible two-digit odd number.

Enter the biggest two-digit number you can think of that uses the digit: