If Today Is Monday, what will be the day after 21 days

How do we solve it ?

A week has 7 days " Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday ".

21 / 7 = 3 ( Remainder = 0)

So you can say that after multiples of 7 days, the day will repeat itself as monday.

Hence after 21 days Monday will occur again.

So we calculate after the remainder (0) , the answer is Monday.

Simple Logic = And whatever the remainder obtained is, add that to the day.