Question

A number when divided by 5 leaves 3 as remainder. What will be the remainder if the square of this number is divided by 5 ?

Answer 1

let the number be x 

x=5k+3

x²=(5k+3)²

=(25k²+30k+9)

= 5(5k²+6k+1)+4

∴ the answer is 4 

dividing x² by 5 we will surely get 4 as remainder