Quicker Maths

How to Find Square of Numbers Ending in 9

Posted on April 1, 2012

Squaring any number ending in 9

We can easily calculate the square of any number ending in 9 using the method described in this post. Let us understand this method with the help of an example –

Finding the square of 39

Firstly add 1 to the number. The number now ends in zero and is easy to square.
40^2 = (4*4*10*10) = 1600. This is our subtotal.

In the next step, add 40 plus 39 (the number we squared plus the number we want to square)

40 + 39 = 79

Subtract 79 from 1600 to get an answer of 1521. To easily do such subtractions, subtract 80 (1 more than 79) from 1600 to get 1520 and then add 1 to get the answer as 1521.

1600 – 79 = 1521 is the square of 39. Answer.

Another Example of finding the square of bigger number ending in 9.

Finding the square of 159

159^2 =
159 + 1 = 160
160^2 = 25600
160 + 159 = 319
25600 – 319 = 25600 – 340 + 1
25600 – 319 = 25281

Another Example,

449^2
450^2 = 202500 (use the shortcut Squaring number ending in 5 to calculate 45^2 and then put double zeroes in front of the answer)
450+449 = 899
202500 – 899 = 202500 – 1000 + 101 = 201601

To make sure that you have understood the above calculation shortcut, try finding the square of few numbers ending in 9 by yourself – 39, 119, 349.

You may also like:

  1. Trick to Find Square of Numbers from 51 to 59
  2. Finding Square of Number Ending in 5
  3. Shortcut to Find Square of a Number

Posted by Vineet Patawari

Comments (10) Trackbacks (0)
  1. Farooqi ji excellant

  2. There is also another method for the same:-

    Square of 19
    i) Subtract 1 from the number ; 19-1 =18
    ii) left the right hand side 9 from the given number; so from 19; 1 will become balance.
    (iii) in the result of (ii) add 1 i.e. 1+1 =2
    (iv) multiply the result of (i) with result from (iii) i.e. 18*2 =36
    (v) write 1 on R.H.side of the answer of (iv) i.e. write 1 with 36 it will 361

    So (19)2 = 361

    similarly for (49)2=

    i) 49-1 =48
    ii) 4+1 =5
    iii) 48*5 = 240
    iv) write 1 on Right Hand side of the result of (iii)
    So answer = 2401.

  3. very nice to solve

  4. thank u very much…

  5. Sir thank you very much.

  6. Give something new information.
    This old stuff is known to everybody.


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