7/24/2019 Math Tricks.pdf

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Interesting Math Tricks

M Vanitha, PRT

1.Instant Multiplication

Lets begin with one of my favorite feats of mental mathhow to multiply, in your head, any

twodigit number by eleven. Its very easy once you know the secret. Consider the problem:

32 x11

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 x11

Since 5 + 3 = 8, your answer is simply 583

2. Sum of all the numbers between two given digits

Add together the first number and the last number in the sequence then multiply by the

number of the middle number in the sequence.

I will try to explain say you wanted to find out the total of numbers 7 to 35.

i.e., 7+8+9 +10+11++33+34+35.

First add the first number in the sequence to the last number in the sequence, which in this

case is 7 + 35 = 42

Then to find the number of the middle digit in the sequence you deduct the lowest number

from the highest number, add 1 then divide by 2

i.e., 35 7 = 28 + 1 = 29 divided by 2 =14.5

Now multiply 42 X 14.5 = 609

So the sum of all figures between 7 and 35 = 609

3.To check if addition is correct

Add up the single digits of each individual number in the sum, until you are left with a

single digit.

Add these single digits together until you are, once again, left with a single digit.

Do the same with the total

These figures should be the same

EXAMPLE: 7745 + 3289 = 11034

7+7+4+5 = 23 2+3 = 5

3+2+8+9 = 22 2+2 = 4

9

1+1+0+3+4 = 9