Speed Mathematics by Bill Handley

Author:Bill Handley [Unknown]
Language: eng
Format: epub, mobi, pdf
Publisher: John Wiley & Sons, Ltd.
Published: 2011-12-01T21:00:00+00:00

Calling out the answers

Giving children these problems (and doing them ourselves) will develop basic number skills. Children of all ages will become very quick at calling out the answers.

If someone were to ask you to multiply 77 by 11, you would immediately see that 7 plus 7 equals 14, which is more than 9. You would immediately add 1 to the first 7 and call out, ‘Eight hundred and . . .’ The next digit will be the 4 from the 14, followed by the remaining 7, so then you could say, ‘. . . forty . . . seven’. Try it. It is much easier than it sounds.

Here is another example: if you had to multiply 84 by 11, you would see 8 plus 4 is more than 9, so you would add 1 to the 8 and say, ‘Nine hundred and . . .’ Now we add 8 and 4, which is 12, so the middle digit is 2. You would say, ‘. . . twenty . . .’ The final digit remains 4, ‘. . . four’. Your answer is, ‘Nine hundred and twenty-four’.

How about 96 × 11?

Nine plus 6 is 15. Add one to the 9 to get 10. Work with 10 as you would with a single-digit number: 10 is the first part of the answer. Five is the middle digit and 6 remains the final digit. The answer is 1056.

If you were doing this problem in your head, you would visualise, ‘Nine plus one carried is ten’. Out loud you would say, ‘One thousand and . . .’ You would then see that the 5 from the 15 is the tens digit, so you continue, ‘. . . fifty . . .’ The units digit remains the same, 6. You can then give the answer, ‘One thousand and . . . fifty . . . six’. Or you could say, ‘Ten. . . fifty-six’.

Try these for yourself. Call out the answers as fast as you can.

a) 37 × 11 =

b) 48 × 11 =

c) 76 × 11 =

d) 92 × 11 =

e) 82 × 11 =

f) 66 × 11 =

The answers are:

a) 407

b) 528

c) 836

d) 1012

e) 902

f) 726

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