# How can we measure 16 minutes with 2 hourglasses running together?

+1 vote
327 views

There are two hourglasses. The small one can measure 5 minutes and the large one can measure 7 minutes.
How can we measure 16 minutes with 2 hourglasses running together?
(If one of the hourglasses finishes leaking, then it must be flipped over immediately to keep it running. )

posted Sep 11, 2014

Start both hourglasses at the same time. You flip over the small hourglass when it finishes the first 5 minutes. Then you flip over the large one when it finishes its first 7 minutes. When the small hourglass runs to 10 minutes, flip over the small and large hourglass at the same time. It means the large hourglass will run 3 minutes again. When the large hourglass run to 13 minutes (7 + 3 + 3), flip both the small and large hourglass over again to run another 3 minutes.

Similar Puzzles

There are two candles. Both will only burn exactly for an hour.
How will you use these two candles to measure forty-five minutes?

+1 vote

Rohan is on his way to visit his girlfriend, who lives at the end of the state.It's her birthday, and he want to give her the cakes that he has made.Between his place and her girlfriend's house, he need to cross 7 toll bridges.
Before you can cross the toll bridge, you need to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake.

How many cakes do Rohan have to carry with him so he can reach his girlfriend's home with exactly 2 cakes?