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Usefulness of Mental Math

Developing numeracy skills early gives children a foundation for their learning and development. It prepares them for daily life, including general problem solving and handling money. Maths includes noticing numbers, shapes, patterns, size, time, and measurement.

Mental math is a group of skills that allow people to do math “in their head” without using pencil and paper or a calculator. Mental math is useful in school and in everyday life. Mental math can help kids understand math concepts better and get to the answer faster.

LEFT TO RIGHT: The “right” way to do mental math.

RIGHT TO LEFT: The “wrong” way to do mental math.

INSTANT MULTIPLICATION

Let’s begin with one of my favorite feats of mental math—how to multiply, in your head, any two-digit number by eleven. It’s very easy once you know the secret. Consider the problem:

32 x 11

To solve this problem, simply add the digits, 3 + 2 = 5, put the 5 between the 3 and the 2, and there is your answer: 352

What could be easier? Now you try:

53 x 11 Since 5 +3 = 8, your answer is simply

583

One more. Without looking at the answer or writing anything down, what is

81 x 11?

Did you get 891? Congratulations!

Now before you get too excited, we have shown you only half of what you need to know. Suppose the problem is

85 x 11

Although 8 + 5 = 1 3 , the answer is not 8 1 3 5 !

As before, the 3 goes in between the numbers, but the 1 needs to be added to the 8 to get the correct answer:

935

Two Digits Multiplication

In the case of two digits by two digits multiplication – if the first digit of both numbers is the same and the second digit of both numbers adds up to 10 it’s very easy to multiply mentally.
Formula: multiply the second digit of both numbers and write the product, then multiply the first digit by an immediate higher number and write before the first product. If last digit of any number is ‘9’ then place a ‘0’ before 9 in the result.

1. 13 x 17 = 3 x 7 = 21
1 x 2 = 2, the answer is 221
2. 22 x 28 = 2 x 8 = 16
2 x 3 = 6, the answer is 616
3. 14 x 16 = 4 x 6 = 24
1 x 2 = 2, The result is 224
4. 71 x 79 = 1 x 9 = 9
7 x 8 = 56, the answer is 5609 (If last digit 9 then place a “0” before 9

By applying this formula you can solve any square ending the number with 5

252
=25 x 25 = 2 x 3 = 6, the answer is 625 (we know that square of 5 is 25 so no need to calculate)
352
=35 x 35 = 3 x 4 = 1225
852
=85 x 85 = 8 x 9 = 7225
1052
=105 x 105 = 10 x 11 = 11025
1152
=115 x 115 = 11 x 12 = 13225

SEE DETAIL COURSE IN COURSE CONTENTS

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