The cakes on display in a bakery are arranged in rows and columns. There are 15 cakes in five columns. How many rows of cakes are there?
The first piece of information that we’re told in this problem is that the cakes on display in a bakery are arranged in rows and columns. The word we could use to describe the way that they’re set out is an array. The word array means exactly what the question says. It’s when items are arranged in rows and columns. Now, there are two things that we can say about arrays. The first is that they always make a rectangle shape, often an irregular rectangle, but sometimes a square. And the second thing we can say is that there a good way of representing multiplication and division facts.
In this example, our array has two rows of four; that’s eight altogether. Two times four is eight. Let’s use our knowledge of arrays to help us solve this problem. The next fact we’re told is the number of cakes that are in the bakery altogether, and that’s 15. There are 15 cakes. We’re told that they’re arranged in five columns. These lines represent the five columns. But we don’t know the number of rows we’re asked. How many rows of cakes are there? In other words, we need to find out how many groups of five there are in 15. So to solve the word problem, we can see that we need to find the answer to a division number sentence, 15 divided by five equals what.
Let’s build up an array using counters, and at the same time we’re going to skip count in five to find out how many five there are in 15. One row of five equals five. Two rows of five equals 10. Three rows of five equals 15. So we can see that we’ve skipped counted in fives three times to get to 15. Five, 10, 15. The number of fives in 15 is three. So we can say 15 divided by five equals three. If there are 15 cakes in a bakery and they’re arranged in five columns, then we know that the number of rows of cakes will be three.