Square a number ending with 5

[srinivasanyadhav]

5^2 = 25
15^2 = 225
25^2 = 625
35^2 = 1225
45^2 = 2025
55^2 = 3025
125^2 = 15625
An easy way to do this is :

Eg : 35^2 = (3*4) / 5*5 = 12 / 25 = 1225
45^2 = (4*5) / 5*5 = 20 / 25 = 2025
125^2 = (12*13) / 5*5 = 156 / 25 = 15625

i.e : a5 *a5 = a(a+1)/5*5

[HansV]

That's an old but useful method for calculating those squares. Thanks.

[Rudi]

That's an old but useful method for calculating those squares...

Is using your smart phone the new method?

[HansV]

That, or the Windows calculator, or Excel, ...