Easy Multiplication of numbers around 100

Multiplication of two numbers around 100 is even easier than you could ever imagine.

Suppose you want to multiply any two numbers, lets take 95 and 97 for example.

Step 1: We'll find out the difference of the two numbers (95 & 97) from 100.

              95 is 5 less than 100 [100-95=5],

               97 is 3 less than 100 [100-97=3].

Step 2: Subtract the total difference from 100. Here the total difference will be 8 [Since 5 + 3 = 8]

               So after subtracting , we get 92 [ 100 - 8 = 92 ]. This becomes first part of our answer.

Step 3: We multiply the two difference amount i.e. 5 & 3 to get 15 as the second part of our answer.

So our final answer becomes 9215. Easy isn't it ?

If you still didn't get it , here's another example for you.

Suppose you mulitiply 88 & 96.

Step 1: Difference of the two numbers ( 88 & 96 ) from 100 are 12 and 4 respectively.

Step 2: Subtracting the total difference of 16 [100- (12 + 40)] from 100 we get 84. [100 - 16 = 84]. So 84 becomes the first part of our answer.

Step 3: Now, we multiply the two difference amount of 12 & 4 to get 48 as second part of our final answer.

So the final answer becomes 8448 .

Self-Exercises:-

a) 92 x 93 =   

b) 94 x 98 =

c) 88 x 85 =

d) 87 x 99 =

Answers: a) 8556 (b) 9212 (c) 7480 (d) 8613 .

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Mental Calculation of Subsequent number 's Square

It is practically easy to calculate the square of the subsequent number if you know the square of the number.
For example, if you know the square of 10, You can figure out the square of 11 mentally and instantaneously.
Here is how you can do it.
Continuing the above example, Square of 10 is 100, So, square of 11 will be 121.
How ???

First, we multiply 10 with 2 to get 20 and add 1 to it to get 21. [We used: 2A + 1 ( Where A is 10 here)]
Next, we add 21 to 100 (Because 100 is the square of 10)

Similarly, if we want to calculate 51², then
We, Know 50²=2500;
So, 51²= 2500 + (2 x 50) + 1
= 2500 + 100 + 1
= 2601 (Easy, isn't it ?? )

Theory behind it-
(a + b)²= a² + 2ab + b² 

If we know a²,  and b is  1 , then  , formula becomes

(a + 1)²= a² + 2a + 1

So, its very easy to solve such square in your head alone. You can do it mentally with a little practice.

Self Exercises:-

a) 61²=
b) 13²=
c) 71²=

Note: This method can also be used for numbers which are not subsequent, this can be dont by placing any other number in place of "b" in the formula.

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Easy Multiplication of a number with 5

It may be difficult for you to multiply a number with 5 , specialy larger numbers like "34638445" , "43574683", or even more larger than this. But after you learn this technique, you can even multiply larger numbers than the above mentioned numbers.
Here is how you should go:
Suppose, You want to multiply 264 with 5, then..

write or imagine mentally:

 [ Note: We have replaced the value of "5" with "10/2" ]

=>2640 / 2= 1320 [ You can mentally divide any number with 2, just move from lefthandside first number to righthandside last number, in this example, we should take "2" as the first number , as "2640" is what we have to divide with 2, so start dividing the numbers mentally, start putting the final answer in our mind, like in this example, start dividing "2" ,"6","4" and "0" with 2, and write or imagine the final answer as 1320. ]

If you still didn't get this principle, for You I am putting more examples for you to cover any aspect that is possible.

More Examples:-

563254 x 5 = 563254 x ( 10/2 ) = 5632540 / 2 = 2816270 (final answer)
You can do this mentally in one step once you master the practise.
In this example, you can directly imagine a zero in the end of the number which you want to multiply 5 with ( This is because, when you multiply any number with 10, the number remains the same and gets an additional zero at the end of the number, for example 1265 x 10 = 12650 , 2485x 10 = 24850 and "M" x 10 = M10 , where M can be any digit or number ), and then you can divide it by 2 in your head mentally or even write at a paper , whichever you feel comfortable with.
The process is the same for multiplying any bigger numbers with 5.
Self-Exercises :-
a) 48662 x 5 = ?
b) 1548994 x 5 = ?
c) 3397551 x 5 = ?

If You still have any doubt, be free to leave a comment here with your name and email id, I'll contact You soon.


You might also like this post: Easy way to multiply numbers around 100 and Easy Numbers' Multiplication with 11 ..

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Easy Multiplication with 9 ( The Finger Rule)

This method is applicable for multiplying 9 with numbers upto 10 .
This method requires the use of your hands, this method is very easy to learn.
This method covers a very limited amount of numbers (i.e numbers ranging between 0 - 10 ) But You'll definately find it very interesting and easy..

Here is how to do it-

Firstly, Spread your hands in front of you.
Now suppose you want to multiply 4 with 9, then fold down the 4th finger from your left.

Now notice that there are 3 fingers on the left of your folded finger, and 6 fingers from the right of your folded finger. So the answer becomes 36.
Apply the same method for multiplying any other number between 0 to 10 .

Self-exercises:-

a) 9 x 5 =
b) 9 x 7 =
c) 9 x 9 =
d) 9 x 4 =

If you liked it leave your comment below...

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