20 August 2013

MATH MAGIC

20 August 2013

MULTIPLICATION TRICKS

CROSS-MULPLICATION

14 X 12

First, to get the last digit in the answer, multiply the two numbers on the right. Write the answer, as the rightmost digit in the problem’s answer.

2x4=8

14 X 12

8

Now, get the middle digit, cross-multiply both sets of numbers, and then add the together.

1 x 2 = 21 x 4 = 4

6

14 X 12

68

Lastly to get the last digit, simply multiply the left digits.

1 x 1= 1 14 X 12

168

TRY!

28 X 23In this case, we will do the carrying

procedure.

COMPLEMENTARY MULTIPLICATION

96 x 94

First, subtract both numbers in 100 and list the difference.

100 - 96 = 4 100 - 94 = 6

Second step is to subtract diagonally. You will notice there that they will give the same answer, and this will be your base number.

96 – 6 = 9094 – 4 = 90

96 x 94

90

Third, multiply the two numbers we got by figuring the difference between the original numbers and 100.

4 x 6 = 24

•Lastly, write it to the right of the base number.

96 x 94

9,024

•If the number are larger than 100, add the difference instead of subtracting.

Ex. 103

x 107

103 – 100 = 3 107 – 100 = 7

103 + 7 = 110107 + 3 = 110

•You will arrive with same answer then write it as the base number.

103 x 107

110

•Multiply the 3 and 7, then write it as the base number.

3 x 7 = 21

103 x 107

11,021

This method is applicable also in numbers around 50.

Ex.

46 x 44

MULTIPLYING BY 11

18X 11

•Add the two digits and insert the sum between the digits.

1 + 8 = 9

18 X 11

198

99 X 11

In case that you got a two-digit number, add that numbers’ left digit to the digit in the original number.

9 + 9 = 18

99 X 11

1,089

SQUARING TRICKS

Squaring a number around 100

If the number falls under 100 and above 50, you simply figure the difference between 100 and the number.

96²

•Subtract the difference from the number being squared, and write the answer as the first digits in your answer.

100 – 96 = 4

96² - 4

92 base number 92(00)

•Take the difference between 100 and the number being squared and square.

100 – 96 = 44² = 16

•Place that number after the base number and you have the answer.

96² = 9,216

If the number to be squared is more than 100, add the difference to the number.

Squaring numbers that ends in 5

Any number that ends in 5 is easy to square to start with, you know that

5 x 5 = 25, so the answer will automatically end in 25.

Ex. 35²

•Add 1 to the first digit, ignore the rest at the number.

1 + 3(5)

4

•Multiply the result to the first digit of the original number. This result is the first part of the answer.

4 x 3 = 12

12 with 25 makes 1, 225.

Try! 85² 115²

65²

SHORTCUT AND HELPFUL HINTS

18 X 101 = 1,81884 X 101 = 8,48497 X 101 = 9,797

102 X 101 = 10,302621 X 101 = 62,721

Thank you!