Magic Maths

Multiplying any number made of digit 9.

Ravindra Koshti — Sat, 27 Mar 2010 13:05:07 +0000

friends I am giving here a simple formula created by me for multiplication of any number made of digit 9 with any other number.
for example take 99 on first instant. I am asked to multiply it by 8. Its very simple and you can do it orally.
1) Multiply 9 with 8. We will get the answer as 72.
2) Now write 72 keeping some space in between.
3) Now add 7 and 2 we will get 9.
4) Write 9 for one time in between 7 and 2, since there are 2 digits in given number.
5) the answer will be 792.
You might have understood the formula.
Now take another example. Consider a Number 99999 to be multiplied by 9.
Step 1 ) 9×9= 81
2) 8 1
3) 8+1=9 write 9 in between 8 and 1 for 4 times since there are 5 digits in given number.
You answer will be 899991

Square of any number ending by 5

Ravindra Koshti — Sun, 22 Nov 2009 05:44:43 +0000

I would like to introduce you a simple formula for getting square of any number ending 5.

(x5)2= x*(x+1)25 This is the formula.

Here x is the digit prefix to 5 of the given number. On right hand side x*(x+1) is only prefix to 25.

Suppose 25 is the given number. Hence x=2

to get square of 25 write 25 on right hand side.

Now multiply 2 by (2+1) i.e. 3, we got 6. Write this 6 as prefix to 25. Here is the answer 625.

Now consider 105 as a given number which is to be squared.

First write 25 on right hand side. Now multiply 10 by 11. We got 110. Write 110 at the left side of 25 the number is 11025. This is the square of given number 105.

We can try with another number. Take 175.

As explained earlier write 25 at right side. Now multiply 17 by 18 answer is 306, write it as prefix of 25, the answer is 30625.

Cross check is with the help of calculator.

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Ravindra Koshti — Mon, 16 Nov 2009 15:02:42 +0000

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Square of any number made of digit 6

Ravindra Koshti — Sun, 15 Nov 2009 18:04:11 +0000

Today we will see how to get square of any number made of digit 6. Let us assume one number 6666. To get square of this number we have to execute following steps.

1) Write down square of 6 i.e. 36 keeping some gap in between both the digits.

Step 1

2) Count how many 6 are there in the given number. Here there are 4 digits.

step2

3) Subtract 1 from 6 and we got 5 which we have to write down to the left of 6 for 3 times i.e. 1 less than above 4.

step3

4) Now add 1 to 3 and we got 4 which we are supposed to write down to the left of 3 for 3 times similar to 5 which we had already written.

Step4

5) The result we got is like this

44435556 which is the square of 6666.

Final Answer

How to multiply any 2 digit number by 11

Ravindra Koshti — Fri, 13 Nov 2009 18:02:22 +0000

It is very easy to multipky any two digit number by 11. Let me explain you how.

Suppose you want to multiply 36 by 11

1) Write 36 keeping some gap between both the digits.

2) Now add both these digits. You will get 3+6=9

3) Write this result of addition in between 3 and 6. You got a number 396.

This is the multiplication of 36 and 11 i.e. 396

You can cross check it with calculator.

Take another number 76

As explained above write 76 keeping some gap between both the digits.

After adding 7 & 6 we get 13

Since the result is a two digit number we must first write 3 between 7 and 6

And the carry over 1 shall be added to first digit of the given number i.e. 7. By addition we got 8.

Now replace pre-written number 7 by 8. Finally we got one number i.e. 836

This is the multiplication of 76 and 11.

Now try it yourself with other numbers.

Good luck.

Getting square of any number made by 3

Ravindra Koshti — Thu, 12 Nov 2009 20:03:12 +0000

We had seen how to get square of any number made by digit 1 easily. Now I would like to show your my simple formula for getting square of any number made by digit 3.

Step 1: Take any number made by digit 3. suppose the number is 333.

Step 2: First write the square of 3 i.e 9.

Step 3: Now by reducing this number 9 by 1 you will get 8. Now count the number of digits in the given number 333. You can see that there are 3 digits in the number. Reduce this 3 by 1. You will get 2. Write 8 for two times to the left of 9.

Step 4: Now simply write zero to the left of last 8 from the right side.

Step 5: Now as we had written 8 for two times write 1 for two times to the left of zero.

Step 6: You got a number as 110889. This is the square of given number 333.

Similarly square of 33333 can be calculated in a fraction of second. It will be 1111088889. Its very simple formula. Try it and give your valuable comments.

Multiplication of any number made of five(5)

Ravindra Koshti — Sat, 24 Oct 2009 19:45:32 +0000

You will find very easy here how to multiply any number made of digit 5 by any given number

Let me explain you how is it possible.

Step: 1 Note down the number made of digit 5 (five) for example we will consider here 55555 as the given number made of five.

Step:2 This number is supposed asked to be multiplied by 7

Step:3 Now multiply 5 by 7. You will get 35

Step:4 Add the digits of the resultant from the multiplication of 7 X 5. after addition 3+5 = 8

Step:5 Now insert 8 in between 3 & 5 which is the resultant of 5 X 7 for 4 times.

I am asking you to insert it for 4 times because total digits in the given number 55555 are five(5) i.e. less than one number.

Step:6 Here you get the result as 388885

This is the answer for multiplication of 55555 X 7

You can cross check it with the help of calculator.

Getting square of any number made by 1

Ravindra Koshti — Tue, 20 Oct 2009 16:00:51 +0000

It is easy to find square of any number made up of digit 1 i.e. 1111, 1111111, 11111111111.

Let me explain you how to find square of these type of numbers.

Step 1. Count the number of digits in the given number. For example take a number 111111 (one lac eleven thousand one hundred and eleven). In this number there are 6 (Six) digits.

Step 2. To get the square of this number write 1,2,3,4,5,6 in sequence like this “123456″ . What we did here is we wrote 1, 2, 3 up to six because there are 6 digits in the given number.

Step 3. Now we should from 6 onwards i.e. 5,4,3,2 and 1 like this”54321″

Step 4. Now the number appears in front of us is ” 12345654321″ This is the perfect square of the given number”111111″

It can be cross checked with the help of calculator.

You can try it with any number