I'm posting one puzzle, riddle, math, or statistical problem a day. Try to answer each one and post your answers in the comments section. I'll post the answer the next day. Even if you have the same answer as someone else, feel free to put up your answer, too!
Friday, September 02, 2005
Do you know what the time is?
You have two hourglasses: a 7 minute one and an 11 minute one. Using just these hourglasses, accurately time 15 minutes.
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Start them at the same time. When the 7 minute one runs out, you've got 4 minutes in the 11 minute timer. Flip them both. When the 4 minutes runs out, you've got 3 minutes in the 7. Let the 11 minute run out. Flip them both again. When the 3 minutes runs out, stop the 11. You now have the 7 minute timer and 8 minutes of sand in the 11 minute one for a grand total of 15 minutesReplyDelete
Or, you could run to Wal-Mart and grab a cheap digital watch for $5 and avoid word problems altogether. :)
I hate Wal-Mart! I'd much rather head out to Target! ;-)ReplyDelete
Flip over both the seven minute hourglass (S) and the eleven minute glass (E) at the same time. When S is done, there are 4 minutes left in E. Flip over S immediately. When E is done there is 3 minutes left in S. Flip over S for another 4 minutes. That's 7+4+4 = 15.
Start the 7 minute and the 11 minute at same time. When the 7 minute one runs out, you've got 4 minutes in the 11 minute timer.ReplyDelete
Forget about 7 minute timer.
Flip the 11 minute timer to consume 4 minutes and then filp it again to measure 11 minutes.
Therefore 4 + 11 = 15
Wow! Someone came in with another answer. Thanks for that, Gaurav!ReplyDelete