Square of numbers ending 5

Here is an example of square of two / three digit numbers ending 5.

We know,

(15)² = 15 X 15 = 225  

(25)² = 25 X 25 = 625

(35)² = 35 X 35 = 1225

and so on…

We might calculate it without calculator for the first two (15 & 25) but what about when number at ten’s place increases. Difficulty starts increasing… Right…

No Worries… Very basic rule, you need to remember…

Rule:

Take first digits (excluding 5) as ‘n’ and multiply it with ‘n+1’ and suffix ‘25’ to the result.



That’s it!!! Is it so simple??? Yeah… Wanna try… Go ahead…

(1 5)² = 1 X (1+1) / ‘25’ = 225

(2 5)² = 2 X (2+1) / ‘25’ = 625

(3 5)² = 3 X (3+1) / ‘25’ = 1225

……………………………………


(7 5)² = 7 X (7+1) / ‘25’ = 5625

(9 5)² = 9 X (9+1) / ‘25’ = 9025

(10 5)² = 10 X (10+1) / ‘25’ = 11025

(12 5)² = 12 X (12+1) / ‘25’ = 15625

(19 5)² = 19 X (19+1) / ‘25’ = 38025

Try it with your calculator… You will find it correct every time…