Math Riddles

Question: A mother is 21 years older than her child. In 6 years the mother will be 5 times older than her baby.

Where is the father?

Question: Why are manholes round instead of square?

Question: A grandfather has a broken grandfather clock that is off by a minute every hour (too fast). He figures out a way, while keeping it running at the same rate, to make the clock say the correct time twice a day.

How could he do this?

Question: Two boys, Trevor and Tyler, are running a 100 meter race. The first time they race Trevor beats Tyler by 5 meters. To make things fair, the next time they race Trevor stands 5 meters behind the starting line.

Who wins the second race (assuming they run the same speed as the first race)?

Question: The warden of a circular jail is extremely hyper one day so he begins running around opening cells. The jail has 100 cells numbered from 1 to 100. He runs in a circle and opens all of the cells. Next he runs around and closes every 2nd cell (starting with cell 2, 4, 6 , etc.). If a cell is open he closes it and if a cell is closed he opens it. When he finishes running by all 100 cells he opens/closes every 3rd cell (starting with 3, 6, 9, 12 etc.), then every 4th cell (starting with 4, 8, 12, etc.) and so on. He does this until he goes around and only changes the 100th cell.

When he is done what cells will be open?