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Puzzle Time
Started by: jo anne (31509)   Report abuse
You have a couple of glass sand timers. One takes seven minutes for the sand to trickle through and the other takes eleven minutes for the sand to trickle through. Using these two, can you time a 15-minute passage of time, exactly?

(Taken from Johnny Ball's book - Ball of Confusion)

Posted by: veg grower (inactive) Report abuse
This reminds me of those quizzes on Professor Layton (not everyone may have heard of that) I don't think I could get it right without any help but will mull it over

Posted by: dostaf (inactive) Report abuse
I only can get 14.

My hands look like I'm doing a 'What's My Line' mime.

EDIT Sorted

7 + 8

Posted by: orrellite (2286) Report abuse
Turn both over when seven has passed turn the 11 one back and when that has finished turn it back for the 11 mins ,

4 plus 11 is 15 mins

Posted by: dostaf (inactive) Report abuse
Imagine the glasses on a swivel, turning them horizontal stops them.

Use the 'seven' to time the 'eleven'

ie stop the 'eleven' leaving four mins sand left (7><4)

Then use that four mins to measure the 'seven'

ie after four minutes, the 'seven' is seperated into four and three minutes. (4><3)

Now you can do the 15 minutes

Use the four minutes, then the 'eleven'

Posted by: jo anne (31509)   Report abuse


Here's Johnny's answer:

"To time 15 minutes exactly, start both sand timers running.

When the 7-minute timer has emptied, turn it over.

When the 11-minute timer has emptied, turn the 7-minute timer over again.

The 7-minute glass will have just run 4 minutes since you last turned it, so it will take 4 minutes to run back again - finish on 15 minutes exactly."

Posted by: dostaf (inactive) Report abuse
Johnny's and Orrellite's way is quicker than mine.

Posted by: jo anne (31509)   Report abuse
You got there in the end though.

(My answer came from the end of the book.)

Veg Grower - my children have got the Prof Layton Nintendo DS games. They sometimes ask me for help, but not often.

Posted by: baker boy (13740) Report abuse
easy peasy

Posted by: jo anne (31509)   Report abuse
Lemon squeezy?

My son's just solved it - Johnny's way - in a matter of minutes, but he is quite mathematically minded.

Posted by: veg grower (inactive) Report abuse
I completed the first Professor Layton, just not got round to doing the others yet. There is something slightly sinister about those - I love 'em.

I'm not a genius at Maths, but I was always well ahead in English. It would have taken me ages to work out that puzzle yesterday.

Posted by: i-spy (13330)  Report abuse
more puzzles needed

Posted by: jo anne (31509)   Report abuse
Taken, again, from Johnny Ball's book - Ball of Confusion:

7. I have three pairs of socks - a blue pair, a green pair and a red pair. I want to hang them on a washing line, but in a puzzling mathematical way.

I want to hang them so that:

There is 1 sock between the blues
There are 2 socks between the greens
There are 3 socks between the reds.

In what order on the washing line should I place them?

Posted by: i-spy (13330)  Report abuse
there will be socks all over the place when the grandkids arrive.
that should keep 'em occupied. Ta jo anne

Posted by: jo anne (31509)   Report abuse
'Heres a similar one but with 4 pairs of socks.

8. You have 4 pairs of socks, blue, green, red and yellow. Hang them on the line so that:

There is 1 sock between the blues
There are 2 socks between the greens
There are 3 socks between the reds
And there are 4 socks between the yellows.

Posted by: i-spy (13330)  Report abuse
I now have yet another sock crisis.And no answers. But they did promise to send me a text.

Posted by: i-spy (13330)  Report abuse
I'm still waiting for answers.
In Jo Anne's absence I'll have to ask Mr Ball

Posted by: jo anne (31509)   Report abuse
Mr Ball's answers

Posted by: i-spy (13330)  Report abuse
Now why didn't I get that

 
 
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