Sue wants to buy 10 rolls of wallpaper. She sees these prices.
Wallpaper
Single roll
£9.21
Pack of 3 rolls £25.38
Pack of 5 rolls
£42.85
What is the cheapest price for 10 rolls?
Your final line must say, Cheapest price is £.
...

This law is sometimes called the grouping property. as you can see, regardless of how the numbers are grouped, the answer is still 13. the associative law of multiplication is similar to the same law for addition. it says that no matter how you group numbers you are multiplying together, you will get the same answer.