Riddle: You have two hourglasses--a 4-minute glass and a 7-minute glass. You want to measure 9 minutes. How do you do it?
Ans: Start both hour glass.. when the 4 min glass runs out, turn it over (4-mins).. then when the 7 min glass runs out, turn it over (7-mins).. when the 4 min glass will run out again (8-mins), turn the 7 min glass.. Now as the 7 min glass has only run for 1 minute previously, when it runs out , you've reached 9 minutes.
minutes..ú yehey!