Learn & Practice Online Maths, English & Science from Ajtlearning.com

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Learn Mathematics TRICKS From AJT Learning.com
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Today we will learn some cool math tricks.
So that, we can use more our brain and less our
calculator.
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Square a two digit number ending in 5
For example 152, 452, 852
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Square a two digit number ending in 5

• Lets consider the number 35.
• 1. We take the first digit and multiply it with
  its next
• number.
• 3 5
• 3 4 12
• 2. Then simply put 25 after it.
• 1 2 2 5

So, 352 1225
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Square a two digit number ending in 5

• Here is another example
• Step-1
• 9 5
• 9 10 90
• Setp-2
• 9 0 2 5
• So, 952 9025

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Multiply any number by 4
Simply double the number two times.
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Multiply any number by 4

• Take the number 63
• 634 63(22) (632)2 1262 252

Lets try another number 753 double of 753
1506 double of 1506 3012 So, 753 4 3012
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Multiply any number by 5
Simply half the number multiply it by 10.
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Multiply any number by 5

• Take the number 86
• 865 86(10/2) (86/2)10 4310 430

Lets try another number 495 half of 495
247.5 247.5 10 2475 So, 495 4 2475
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Multiply any number by 15
Multiplication by 10 Multiplication by 5.
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Multiply any number by 15

• Take the number 84
• 8410 840
• 845 (84/2)10 4210 420
• 8415 840 420 1260

Lets try another number 495 49515 49510
4955 4950 (495/2) 10
4950 2475 7425
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Multiply any number by 11
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Multiply any number by 11
Take the number 263
Lets try another number 485
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Multiply two numbers between 10 and 20
For example 1517, 1913
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Multiply two numbers between 10 and 20

• Lets consider the number 1214.
• 1. Add the first number with the other numbers
• second digit.
• 1 2
• 1 4
• 1 6
• 2. Place a 0(zero) after it.
• 1 6 1 6 0

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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 8 1 6 8
So, 1214 168
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Multiply two numbers between 10 and 20

• Here is another example 1713
• Step-1 17 3 20
• Setp-2 20 200
• Step-3 7 3 21
• Step-4 200 21 221
• So, 1713 221

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Divisibility Check
For example is 7403 is divisible by 11 ?
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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 729 which is divisible by 3.
• Another example 57381, 5738124 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 - (12) 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 22 371 37 12 35
Now, 35 is divisible by 7. So, 3752 is also
divisible by 7. You may have gone even further,
35 3 - 52 -7 which is
also divisible by 7.
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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 0
• So, it is divisible by 11.
• Take 392755
• 3 - 9 2 - 7 5 - 5 -11
• Also divisible by 11

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Divisibility Check (for 13)

• For 13, add 4 times of the last digit to the rest
  of the number. Take 351
• 351 3514 39
• It is divisible by 13.
• Lets try another 754
• 754 75 44 75 16 91
  914 13
• So, you know.

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So we have leant a lot of math tricks today.
Practice to make them perfect for you.
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There is one math trick only for YOU!
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Lets see if you can do it right!
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Add these numbers one after another-
1000 20
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Add these numbers one after another-
1000 20 1000 30
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Add these numbers one after another-
1000 20 1000
30 1000 40
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Add these numbers one after another-
1000 20 1000
30 1000 40 1000 10
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Add these numbers one after another-
1000 20 1000
30 1000 40 1000
10 5000 ???
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Add these numbers one after another-
1000 20 1000
30 1000 40 1000
10 5000 ???
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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