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Posted 20 April 2008 - 04:10 AM
1. First, run both the sand-glasses..
2. After 7-min, flip the 7-min sand glass and let the 11-min flow..
3. Again after 4 more minutes, flip the 7-min sand-glass again..
Thats it !! 7+4+4=15..
Posted 16 May 2008 - 12:40 PM
Sand-glass II. - Back to the Water and Weighing Puzzles
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.Spoiler for Solution
All very good I see that it works - just one problem you turn the sand glass over four times not three - twice to get the 7 & 11 going then when the 7 finishes you turn that once more and that is now three - when the 11 runs out you need to turn the 7 back over to get the four minutes that it has just used and that makes four turns.
Samuelpt you seem to be ignoring the two times to set both A11 and B7 off
Posted 28 October 2008 - 10:34 PM
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