Dividing in your head

If you have memorised some division and multiplication tables, you can use them to divide in your head. Here are some examples of how you might solve problems:

·         42 ÷ 7

You could recall the 7 times table and remember that 7 x 6 = 42 to get the answer 6.

·         47 ÷ 9

You could recall that 45 ÷ 9 = 5 and count on from 45 to 47 to get the answer 5 remainder 2.

·         600 ÷ 8

Because 8 = 2 x 2 x 2, you could divide 600 by 2 and then divide by 2 again, and then divide by 2 again.

600 ÷ 2 = 300

300 ÷ 2 = 150

150 ÷ 2 = 75

·         67 ÷ 10 and 4.3 ÷ 10

To divide a number by 10, move the digits one place to the right, adding a zero if necessary.

67 ÷ 10 = 6.7

4.3 ÷ 10 = 0.43

·         290 ÷ 100 and 4.3 ÷ 100

To divide a number by 100, move the digits two places to the right, adding zeros if necessary.

290 ÷ 100 = 2.9

4.3 ÷ 100 = 0.043

·         24 ÷ 20

To divide by numbers such as 20, divide by the 2 first and then by the 10.

24 ÷ 2 = 12

12 ÷ 10 = 1.2

Dividing in your head

If you have memorised some division and multiplication tables, you can use them to divide in your head. Here are some examples of how you might solve problems:

·         42 ÷ 7

You could recall the 7 times table and remember that 7 x 6 = 42 to get the answer 6.

·         47 ÷ 9

You could recall that 45 ÷ 9 = 5 and count on from 45 to 47 to get the answer 5 remainder 2.

·         600 ÷ 8

Because 8 = 2 x 2 x 2, you could divide 600 by 2 and then divide by 2 again, and then divide by 2 again.

600 ÷ 2 = 300

300 ÷ 2 = 150

150 ÷ 2 = 75

·         67 ÷ 10 and 4.3 ÷ 10

To divide a number by 10, move the digits one place to the right, adding a zero if necessary.

67 ÷ 10 = 6.7

4.3 ÷ 10 = 0.43

·         290 ÷ 100 and 4.3 ÷ 100

To divide a number by 100, move the digits two places to the right, adding zeros if necessary.

290 ÷ 100 = 2.9

4.3 ÷ 100 = 0.043

·         24 ÷ 20

To divide by numbers such as 20, divide by the 2 first and then by the 10.

24 ÷ 2 = 12

12 ÷ 10 = 1.2

Writing it down

If the numbers are too difficult to divide in your head, use a written method. This is called long division.

Try 474 ÷ 6:

• 6 doesn't go into 4, so put 0

• 6 into 47 goes 7 times

• 7 x 6 = 42. Take 42 away from 47 to get the remainder of 5.

• Bring down the next digit, the 4

n_division2_4.gif

• 6 into 54 goes 9 times with no remainder

As there are no more digits to bring down, the division is finished.

The answer to 474 ÷ 6 is 79 (with no remainder).

Useful tips

• Estimate first and check afterwards.
• It's a good idea to estimate a rough answer first. And always check your actual answer.
• Division and multiplication are opposites.
• For example, 54 ÷ 6 = 9 and 9 x 6 = 54. So you can use multiplication to check your answer to a division problem.
• A division sum can be shown in different ways.
• You might see 54 divided by 6 shown in any of the ways below.