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.
1
Square a two digit number ending in 5
For example: 152, 452, 852
2
Square a two digit number ending in 5
Lets consider the number 35.1. We take the first digit and multiply it with it’s nextnumber.
3 5
3 * 4 = 12
2. Then simply put 25 after it.1 2 2 5
So, 352 = 12253
Square a two digit number ending in 5
Here is another example:Step-1:
9 5
9 * 10 = 90Setp-2:
9 0 2 5So, 952 = 9025
4
Multiply any number by 4
Simply double the number two times.
5
Multiply any number by 4
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
6
Multiply any number by 5
Simply half the number &multiply it by 10.
7
Multiply any number by 5
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
8
Multiply any number by 15
Multiplication by 10 + Multiplication by 5.
9
Multiply any number by 15
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
10
Multiply any number by 11
x y z
x y + z zx + yxyz * 11 =
11
Multiply any number by 11
Take the number 263
Lets try another number 485
2 6 3
2 9 38263 * 11 =
4 8 5
5 3 53263 * 11 = 11
12
Multiply two numbers between 10 and 20
For example: 15*17, 19*13
13
Multiply two numbers between 10 and 20
Lets consider the number 12*14.1. Add the first number with the other number’ssecond digit.
1 2 + 1 4
1 6
2. Place a 0(zero) after it.1 6 1 6 0
14
Multiply two numbers between 10 and 20
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
Multiply two numbers between 10 and 20
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 ?
17
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.
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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.
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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.
20
Divisibility Check (for 11)
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
21
Divisibility Check (for 13)
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.
23
There is one math trick only for
YOU!24
Lets see if you can do it right!
25
Add these numbers one after another-
1000 20
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Add these numbers one after another-
1000 201000 30
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Add these numbers one after another-
1000 201000 301000 40
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Add these numbers one after another-
1000 201000 301000 401000 10
26
Add these numbers one after another-
1000 201000 301000 401000 105000 ???
26
Add these numbers one after another-
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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