Start both hourglass at same time As 7minutes gets competed,by 11 minutes We remains with 4 minutes Now as soon as 11 minutes hourglass completes ,reverse it We get 11 minutes Finally We get 15 minutes,4 minutes and this 11 minutes

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. )

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