Math Core

You already know that multiplication means equal groups. Now it's time to get fast at the facts. The 2s, 5s and 10s are the best place to start, because each one has a pattern you can spot right away.

Multiplying by 2: doubles

Multiplying by 2 means you have 2 equal groups. That is the same as a doubles fact from adding.

$2 \times 7$ means $7 + 7$ , so $2 \times 7 = 14$ .

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Every answer in the 2s is an even number: it ends in 0, 2, 4, 6 or 8.

Multiplying by 10: add a zero

Counting by tens goes 10, 20, 30, 40, … . So 6 tens is 60. When you multiply a number by 10, the answer is that number with a 0 on the end.

$10 \times 6 = 60$ and $10 \times 9 = 90$ .

Multiplying by 5: half of 10

Count by fives on a number line. Each hop is 5 long.

Six hops of 5 land on 30, so $6 \times 5 = 30$ .

The 5s have two patterns:

Every answer ends in 0 or 5.
5 is half of 10, so $5 \times$ a number is half of $10 \times$ that number. For $5 \times 8$ : $10 \times 8 = 80$ , and half of 80 is 40.

Patterns for 2, 5 and 10

× 2: double the number.
× 10: write the number with a 0 on the end.
× 5: find × 10, then take half. The answer ends in 0 or 5.

$n$	1	2	3	4	5	6	7	8	9	10
$2 \times n$	2	4	6	8	10	12	14	16	18	20
$5 \times n$	5	10	15	20	25	30	35	40	45	50
$10 \times n$	10	20	30	40	50	60	70	80	90	100

Division facts come free

Each multiplication fact gives you division facts too. Since $5 \times 7 = 35$ , you also know $35 \div 5 = 7$ and $35 \div 7 = 5$ .

To divide by 10, take the 0 off the end: $80 \div 10 = 8$ .

Worked example: Double it

What is $2 \times 9$ ?

Double 9: $9 + 9 = 18$ .

$2 \times 9 = 18$ .

Worked example: Half of ten times

What is $5 \times 7$ ?

First, $10 \times 7 = 70$ . Half of 70 is 35.

$5 \times 7 = 35$ .

Worked example: Divide with a fact you know

There are 45 crayons. You put 5 crayons in each cup. How many cups do you fill?

You need $45 \div 5$ . Think: $5 \times ? = 45$ . Count by fives: 5, 10, 15, 20, 25, 30, 35, 40, 45. That is 9 fives.

You fill 9 cups.

Common mistake

Don't mix up $10 \times 4$ and $10 + 4$ . Ten groups of 4 is 40. Adding 10 and 4 is only 14.

Tip

Check a 5s answer: it must end in 0 or 5. If you get $5 \times 6 = 32$ , you know right away something went wrong.

Practice

Practice 1

What is $2 \times 8$ ?

Type a number.

Practice 2

What is $10 \times 7$ ?

Type a number.

Practice 3

What is $5 \times 9$ ?

Type a number.

Practice 4

Which number could be an answer in the 5s facts?

Practice 5

What is $60 \div 10$ ?

Type a number.

Practice 6

What is $40 \div 5$ ?

Type a number.

Practice 7

Nickels are worth 5 cents each. Mia has 9 nickels. How many cents does she have?

Type a number.