Sand Glass II?
A teacher of mathematics used an unconventional method to measure time for a test lasting 15 minutes. He used just a sand-glass, which spills in 7 minutes and a second sand-glass, which spills in 11 minutes. During the whole time he turned sand-glasses only 3 times. Explain how the teacher measured 15 minutes.
MindsEye
on February 6th, 2012
He started them both at the same time (2)
When the 7 minute glass finished, he still had 4 minutes remaining in the 11 minute glass.
Then when the 11 minute finished, he quickly turned it again (3) for a full term of 11 minutes.
He turned the two at the start and the one for a total of three.
There he had the remaining 4 minutes from the start plus the full 11 minutes.
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Fly
on February 6th, 2012
1. Start both the Sand glasses.
2. Once the 7-minute glass spills over, start the test.
3. By the time 11-minutes glass spills over, we would have finished 4-minutes.
4. Once the 11-minutes spills over, turn it over again.
Robert has a flaw in his, if he flips both, waits for the 11 to finish, then flips it again for a full term, thats 22 minutes.
FollowTheLeader
on February 6th, 2012
t= 0:
start both of them
t = 7:
turn over the 7
t = 11:
the 11 runs down, and the 7 has 3 mins to go, which means 4 mins have elapsed from the 7. So turn over the 7, and this will take you to 15 mins
Bambi
on February 6th, 2012
he sets them both going.
When the 7minute hour is emptied , 7 minutes have elapsed and he now turns them both over. When the 11 minute glass is emptied 4 aditional mintes have elapsed for a total of 11 minutes now he turns the 7 minnute glass over and when it is empty another 4 minutes has elapsed for a total of 15 minutes.
glass