Or a ten frame. By using a ten frame you can easily see that 20 is made up of two 10s. You can also see that 11 is one more than 10 and 9 is one fewer, but together they total 20.

There are 10 fingers on these hands, 10 counters in the ten frame, 10 beads on the string, 10 dots on the domino and 10 pencils in the pack. Can you think of some other things that come in 10s?