Question:
Using only a four-minute hourglass and a seven-minute hourglass, what time can be measured with the process not taking longer than the time we are trying to measure.
A) 8 Minutes
B) 11Minutes
C) 6 Minutes
D) 9 Minutes
Solution: A B D are the solutions
For 8 mins,we can use the 4 min hourglass twice.For 11 mins, we can use 4 min hourglass followed by 7 min hourglass.For 9 mins, start both hourglasses at 0 minutes. Flip over the four-minute glass when it runs out (at 4:00); ditto for the seven-minute glass (at 7:00). When the four-minute glass runs out the second time (at 8:00), the seven-minute glass will then have one minute of sand in its lower bulb. Flip the seven-minute glass over again and let the minute of sand run back. When the last grain falls, that will be nine minutes.
