Square of numbers ending with 5
  Formula for calculating square ending with 5 is easy. I have also discussed this multiplication in my multiplication Article.
 
  85
  x
  85
  -------------
  7225  
 
Steps
• Multiply 5 by 5 and put composite digit 25 on the right hand side.
• Add 1 to the upper left hand side digit i.e. 8 i.e. 8+1=9
• Multiply 9 to the lower hand digit 8, i.e. 9*8=72
• Our answer is 7225.

Using this method we can find out square of the number. Now let’s have a look at method of calculating square of adjacent number.


Forward Method
  We know method to find square of a number ending with 5., say Square of 75=5625, then just have a look to find square of 76.
75’s square=5625(known)
76’square=75’square+ (75+76) =5625+151=5776.
So square of 76 is 5776.
Steps
• Steps are simple. The format shown above is self explanatory. But still I am explaining it.
• 75’square=5625 is known
• Add (75+76=151) to this to get 76’square
• 76’square=5776.


 Reverse Method
  As like forward method for calculating square of number which is 1 more than the given number whose square is known, we have reverse method to find square.
  Now let me explain in detail the Reverse approach through which You will able to find out squares of a number which is one less than given number.
Consider the following example:
Suppose we know square of a number, say, 70; how to find square of 69?
(70)’square=4900(known)
(69)’square=4900-(69+70) =4900-139
  =4761.


Mental formula for finding Squares
Let us first find square of 11 using formula:
11’square=11+1/1square=12/1=121.
The formula is self explanatory. However, let me explain it in detail for more clarification.
• The slash is used just as a operator.
• Our operating zone is 10 X 1 or simply 10.
• 11 is more than 10.
• We add 1 to 11to make 12.
• The number of digits after the slash can be only one.
• If the number of digits after the slash exceeds one, then we place only the rightmost digit on the extreme right after the slash, and the remaining gets added to the number on the left hand side of the slash.
• Now have a look at few more examples for better understanding.
12’square=12+2/2’square=14/4=144
13’square=13+3/3’square=16/9=169.
14’square=14+4/4’square=18/16 (Apply step no 6 here) 18/16=18+1/6=196.
15’square=15+5/5’square=20/25=20+2/5=225.
16’square=16+6/6’square=22/36=22+3/6=256.
You can work like this up to 19’square.But for 20 formula is slightly change.
The slight Change in formula as follows:
21’square=2 X (21+1)/1’square= 2 X (22)/1=44/1=441.
This change is because now we are operating in the 10 X 2 Zone. Similarly we can calculate Square of 31 but with slight change as follows:
31’Square=3 X (31+1)/!’square= 3 X (32)/1=96/1=961.
By these methods explained you can easily calculate and memorize the squares of numbers up to 99 with out much hassle.
Master Formula to Calculate Square in 10 Seconds.:
  Till now we have seen various formulae to calculate square of the number. Now I am giving such a master Formula by which you can orally calculate Square of the number with in 10 Seconds.
11’square=121. 12’square=144
111’square=12321 121’square=14641

Steps:
• Consider number 121 to find square.
• Separate digits as 12 & 1.
• Now do Square of unit digit number i.e. 1’square=1, so our unit digit number is 1 now in this case.
• Then multiply both separated Digits which are earlier separated ie.12 & 1
• =12 X 1=12 
• Now double the result of multiplication i.e. Double of 12= 24. And place it left after unit digit number i.e. 2 41.( 2 is Carry)
• Separate carry 2 then
• Now At last square 12 i.e. 12’square=144 and add earlier Carry to it. 
• So we get 144+2(carry)=146
• Finally we obtained Square as 14641..
Let us have a look at one more example.
151’square:
• 1’s square=1.
• 2 x (15 x 1) = 3 0 (Double of 15 and 1 and 3 is carry now.)
• Now 15’square=225+earlier carry i.e.3=228 
• So Final Answer is 22801