Calculate square of number ending with 5

Lets take a number ending with 5. let it be 65

•  Perform 5 × 5 = 25

•  Add 1 to the previous number and multiply this result with the previous number. 

  For example, in the case of the square of 65, Add 1 to 6 = 7 and multiply 7 with 6 = 42

•  The result from step two will become the starting numbers of the final answer and the result of step one is the ending two numbers of the final answer. So the final answer will be 4225.

Now find the square of 115 using same technique.

reference:- Vedic Maths