Year 4AC9M4N06

Multiplication

Develop efficient strategies and use appropriate digital tools for solving problems involving addition and subtraction, and multiplication and division where there is no remainder.

Read this first

Multiplying is counting equal groups. 4 groups of 6 is the same as 6 groups of 4.

This is 4 rows of 6. Count them and you get 24. So $4 \times 6 = 24$ .

Words you need

Array: Dots or squares set out in equal rows.
Product: The answer when you multiply.
Factor: A number you multiply. In $4 \times 6$ , the factors are 4 and 6.

Worked example

e.g. Work out

7 \times 8

Draw 7 rows with 8 in each row.
You do not have to count them all. Use one you know. $7 \times 4 = 28$ .
8 is double 4. So double your answer. $28 + 28 = 56$ .
So $7 \times 8 = 56$ .

If you forget a fact, build it from one you know. Doubling and halving get you there fast.

Practice

The pictures fade as you go. By the last few you are on your own.

1How many squares? Write it as a multiplication.with a picture

Answer15.

3 \times 5 = 15

2How many squares?with a picture

Answer36.

6 \times 6 = 36

3Work out

6 \times 8

.with a hint

Need a hint?

You know $6 \times 4 = 24$ . Now double it.

Answer48.

24 + 24 = 48

4Work out

9 \times 7

.with a hint

Need a hint?

Do $10 \times 7 = 70$ , then take one 7 away.

Answer63.

70 - 7 = 63

8 \times 7

on your own

Answer56

9 \times 6

on your own

Answer54

7A box holds 8 cakes. How many cakes in 7 boxes?on your own

Answer56 cakes.

8There are 6 rows of chairs with 9 chairs in each row. How many chairs?on your own

Answer54 chairs.

Think about it

Why is

4 \times 6

the same as

6 \times 4

One good answerTurn the array on its side. 4 rows of 6 becomes 6 rows of 4. You have not added or taken away any squares, so the answer stays the same.

How does knowing your 10 times table help with the 9s?

One good answerWork out the 10 times fact, then take one lot away.

9 \times 7

70 - 7 = 63

7 \times 8

bigger or smaller than

7 \times 10

? Answer without working it out.

One good answerSmaller. You have 7 lots of a smaller number, so the total must be less.

Common mistakes

Counting every square one by one.

That is slow and easy to get wrong. Use a fact you already know and build from it.

Adding when the question says multiply.

7 \times 8

is 7 lots of 8, not

7 + 8

. Picture the rows.

Thinking

9 \times 7

and

7 \times 9

are different.

They give the same answer. Turn the array round.