I WILL ANSWER THIS

The Teacher asked in the school "boys, a car is running at a speed of 90 kmph, then what is my age?"

All students became stunned. The Little Johny raised his hand and said "Sir, 40 yrs."

Very Good, said the teacher. But how did you calculate?

Little Johny said, There is a half mad person lives in our colony, whose age is 20 years