Squaring a number that ends in 5 is very easy.

This method can be applied to any number of the form: 15, 25, 35, …., 95, 105, 285, …. and so on.

Sutras:

  • By One More Than the One Before

Let’s explore this with an example:

352 3•4 / 25 12 / 25 → 1225

The result is comprised of two “parts”. 

The bottom “part” is always 25. 

The top “part” is n(n+1).

More examples as below:

752 7•8 / 25 56 / 25 → 5625

452 4•5 / 25 20 / 25 → 2025

952 9•10 / 25 90 / 25 → 9025

1152 11•12 / 25 132 / 25 → 13225