This Puzzle is one of the most commonly asked interview puzzle.
You have two sand timers with you. One can measure 7 minutes and the other sand timer can measure 11 minutes. This means that it takes 7 minutes for the sand timer to completely empty the sand from one portion to the other.
You have to measure 15 minutes using both the timers. How will you measure it ?
7 Minutes Sand Timer Finished.
Time Remaining in 11 minutes timer – 4 minutes
Reversing the 7 minutes timer – 4 minutes will elapse. 3 Minutes will left.
Once 11 minutes gets over reverse the 11 minutes timer again to use that 3 minutes. 8 Minutes left.
Now Reverse 7 minutes timer to measure 7+8 = 15 minutes.