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Puzzle Time

Started by: jo anne (32796) 

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)

Started: 11th Jan 2012 at 11:51

Posted by: veg grower (inactive)

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

Replied: 11th Jan 2012 at 13:54

Posted by: dostaf (inactive)

I only can get 14.

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

EDIT Sorted

7 + 8

Replied: 11th Jan 2012 at 15:43
Last edited by dostaf: 11th Jan 2012 at 15:46:08

Posted by: orrellite (2350)

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

Replied: 11th Jan 2012 at 15:48

Posted by: dostaf (inactive)

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'

Replied: 11th Jan 2012 at 16:37
Last edited by dostaf: 11th Jan 2012 at 16:42:53

Posted by: jo anne (32796) 



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."

Replied: 11th Jan 2012 at 16:58

Posted by: dostaf (inactive)

Johnny's and Orrellite's way is quicker than mine.

Replied: 11th Jan 2012 at 17:04

Posted by: jo anne (32796) 

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.

Replied: 12th Jan 2012 at 14:25

Posted by: baker boy (15456)

easy peasy

Replied: 12th Jan 2012 at 15:01

Posted by: jo anne (32796) 

Lemon squeezy?

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

Replied: 12th Jan 2012 at 17:05

Posted by: veg grower (inactive)

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.

Replied: 12th Jan 2012 at 17:19

Posted by: i-spy (14716) 

more puzzles needed

Replied: 15th Sep 2013 at 12:24

Posted by: jo anne (32796) 

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?

Replied: 15th Sep 2013 at 14:49

Posted by: i-spy (14716) 

there will be socks all over the place when the grandkids arrive.
that should keep 'em occupied. Ta jo anne

Replied: 15th Sep 2013 at 15:17

Posted by: jo anne (32796) 

'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.

Replied: 15th Sep 2013 at 15:31

Posted by: i-spy (14716) 

I now have yet another sock crisis.And no answers. But they did promise to send me a text.

Replied: 18th Sep 2013 at 17:49

Posted by: i-spy (14716) 

I'm still waiting for answers.
In Jo Anne's absence I'll have to ask Mr Ball

Replied: 11th Oct 2016 at 22:17

Posted by: jo anne (32796) 

Mr Ball's answers

Replied: 18th Oct 2016 at 09:42
Last edited by jo anne: 7th Jul 2017 at 18:08:32

Posted by: i-spy (14716) 

Now why didn't I get that

Replied: 23rd Oct 2016 at 14:13

 

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