Why do we have to learn this stuff?

I once had a student who knew exactly how long 5 cm was. A teacher had had each student find 5 centimeters somewhere on their hands. Connecting up to prior knowledge?
2 cm is a good deal more than half an inch, though, more than 3/4 inch. I think they need more practice working with rulers!
Here's another reason to learn math.
American Chopper vs The Metric System:
(another reason to learn the metric system)