Problem of the Week
for Friday, Oct 10

 

The priceless Moroccan "Coco" has been stolen!
Luckily, we still have the original mold (which you will recall has a diameter precisely twice that of a US Quarter). If a quarter is rolled completely around the middle of the mold until it returns to its original position, how many full turns does George washington's head make? Please explain.



Elissa's Solution

One.
I made 2 dots on my quarter and 4 dots on my priceless Moroccan "Coco". As you see, Dot 1 and Dot 5 are on the same line. that means when the quarter starts to roll, Dot 5 is going to end up at Dot 1. Then, the quarter will roll more and Dot 6 will end up at dot 2. Then, the quarter will roll and Dot 5 will go to dot 3. Then, to finish the circle, dot 6 will go back to where it started at Dot 4. the quarter has made 1 full turn.

Animation of Elissa's Solution