Eight socks were on the washing line. The wind blew some behind the sheet. Five are still pegged. How many are hiding? How do you know?

A bond is two parts that join to make a number. Look at the washing lines. Every line holds 8 socks. How many yellow socks? How many blue? Beside each line is its bond.

Keep your eye on the whole: it stays 8. Notice what happens to one part when the other part gets bigger.

Now a line of 9 socks, and its bond.

Now we make bonds of 8 on the board. It starts as 4 and 4. Take one counter from one part and give it to the other part. We all say the new bond.

• 8 as 5 and 3
• 8 as 6 and 2
• 8 as 7 and 1

Then 9 of you come to the front and make bonds of 9 with your own bodies. One of you walks across at a time.

• 9 as 5 and 4
• 9 as 6 and 3
• 9 as 7 and 2
• 9 as 8 and 1