Riddle:
Susy is traveling by ship from south of the equator to the north. She has a nice little cabin with a bathroom, but no window. Sally has no compass nor other instruments. Just the general luggage one brings on board a long cruise. Yet, without leaving her room or talking with anyone, Susy will be able to tell when the ship has crossed the equator. How?
Answer: Susy can fill the sink and watch it drain. When the water reverses direction when going down the drain, she will know they have crossed the equator.
Riddle:
How can you measure nine minutes with have two hourglasses, one four minute and one seven minute?
Answer: Turn over both hourglasses at once. When the four-minute hourglass runs out, turn it over. When the seven-minute hourglass runs out, turn it over. When the four-minute timer runs out this time (eight minutes have elapsed), the seven-minute hourglass has been running for one minute. Now turn over the seven minute timer back over. When the timer runs out, nine minutes have elapsed.