Amazing Math Tips & Tricks

transcript

Welcome to the World of MATHEMA-TRICKS

Minhas Kamal

Today we will learn some cool math tricks.

So that, we can use more our brain and less our calculator.

Square a two digit number ending in 5

For example: 152, 452, 852

Lets consider the number 35.1. We take the first digit and multiply it with it’s nextnumber.

3 * 4 = 12

2. Then simply put 25 after it.1 2 2 5

So, 352 = 12253

Here is another example:Step-1:

9 * 10 = 90Setp-2:

9 0 2 5So, 952 = 9025

Multiply any number by 4

Simply double the number two times.

Take the number 6363*4 = 63*(2*2) = (63*2)*2 = 126*2 = 252

Lets try another number 753double of 753 = 1506double of 1506 = 3012So, 753 * 4 = 3012

Simply half the number &multiply it by 10.

Take the number 8686*5 = 86*(10/2) = (86/2)*10 = 43*10 = 430

Lets try another number 495half of 495 = 247.5247.5 * 10 = 2475So, 495 * 4 = 2475

Multiplication by 10 + Multiplication by 5.

Take the number 8484*10 = 84084*5 = (84/2)*10 = 42*10 = 42084*15 = 840 + 420 = 1260

Lets try another number 495495*15 = 495*10 + 495*5

= 4950 + (495/2) * 10 = 4950 + 2475 = 7425

x y + z zx + yxyz * 11 =

Take the number 263

Lets try another number 485

2 9 38263 * 11 =

5 3 53263 * 11 = 11

Multiply two numbers between 10 and 20

For example: 15*17, 19*13

Lets consider the number 12*14.1. Add the first number with the other number’ssecond digit.

1 2 + 1 4

2. Place a 0(zero) after it.1 6 1 6 0

3. Multiply the second digits of the two numbers.1 4

* 1 2 8

4. Add this number with the step-2 result.1 6 0

+ 81 6 8

So, 12*14 = 16815

Here is another example: 17*13

Step-1: 17 + 3 = 20

Setp-2: 20 200

Step-3: 7 * 3 = 21

Step-4: 200 + 21 = 221

So, 17*13 = 22116

Divisibility Check

For example: is 7403 is divisible by 11 ?

Divisibility Check (for 2, 3)

A number is divisible by 2 if its last digit is 0, 2, 4, 6 or 8. For example: 12, 5394, 993120.

A number is divisible by 3 if sum of its digits is divisible by 3. For example: 72 is divisible by 3 as 7+2=9 which is divisible by 3.Another example: 57381, 5+7+3+8+1=24; 24 is divisible by 3. So 57381 is also divisible by 3.

Divisibility Check (for 5, 7)

A number is divisible by 5 if its last digit is 0 or 5. For example: 100, 3795, 698170.

For 7, separate & double the last digit of the number. Then subtract it from the rest. Take: 91.

91 9 1 9 - (1*2) 7

Now, if the number is 0 or divisible by 7, then the original number is also divisible by 7.

Divisibility Check (for 7)

If the number is big then continue the process as many time as needed.

Lets take 3752.3752 375 – 2*2 371 37 – 1*2 35

Now, 35 is divisible by 7. So, 3752 is also divisible by 7.You may have gone even further,

35 3 - 5*2 -7 ; which is also divisible by 7.

For 11, add and subtract digits in an alternative pattern (like- 1st digit - 2nd digit + 3rd digit …).Take: 8525

8 - 5 + 2 - 5 = 0So, it is divisible by 11.

Take: 3927553 - 9 + 2 - 7 + 5 - 5 = -11

Also divisible by 11

For 13, add 4 times of the last digit to the rest of the number. Take: 351

351 35+1*4 39

It is divisible by 13.Lets try another: 754

754 75 + 4*4 75 + 16 91 9+1*4 13

So, you know.22

So we have leant a lot of math tricks today.

Practice to make them perfect for you.

There is one math trick only for

YOU!24

Lets see if you can do it right!

Add these numbers one after another-

1000 20

1000 201000 30

1000 201000 301000 40

1000 201000 301000 401000 10

1000 201000 301000 401000 105000 ???

If your answer is 5000, then you are among the most who mistook. The actual answer is 4100. Count again and see if you get it right this time.

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Amazing Math Tips & Tricks

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