Math Riddles

Question: When is 1500 plus 20 and 1600 minus 40 the same thing?

Question: What is the difference between a dollar and a half and thirty five-cents?

Question: Does an ounce of gold or an ounce of feathers weight more?

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: 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?