Go to navigation
It is currently Sun Dec 11, 2016 10:04 am

All times are UTC




Post new topic Reply to topic  [ 52 posts ]  Go to page 1, 2, 3, 4, 5, 6  Next
Author Message
PostPosted: Sun Nov 25, 2012 7:01 pm 
Offline

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 165
I was wondering if any of you clever people can help me with my daughter's homework. We have been trying to work it out for about an hour and I now give up !

There are 4 jugs, one is a 9 litre ,then a 7 litre, a 4 litre and a 2 litre .
The 9 litre jug is full, the others are empty. We have to work out how to get 3 litres into 3 of the jugs.

Am I being stupid or is it not possible ?

Many thanks in advance of your cleverness !


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 7:20 pm 
Offline

Joined: Mon Jul 04, 2011 1:47 pm
Posts: 2151
Location: Warwickshire
I have no idea at all, but that sounds very much like an 11+ kind of question.

Sorry!


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 7:34 pm 
Offline

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 165
No just year 5 homework. Maths isn't exactly my strong point and despite the name nor is logic !!!


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 7:51 pm 
Offline

Joined: Fri Oct 30, 2009 11:08 pm
Posts: 1226
According to DS (year 10)!
fill 7L jug from the 9L, 2 7 0 0
fill 4L jug from the 7L, 2 3 4 0
fill 2L jug from the 7L, 2 1 4 2
pour 2L into 9L, 4 1 4 0
pour 7L into the 2L, 4 0 4 1
fill 7 L with 4L and 9L, 1 7 0 1
fill 4L with 7L, 1 3 4 1
pour 4l into 9L, 5 3 0 1
pour 2L into 4L, 5 3 1 0
fill 2L from 9L, 3 3 1 2
pour 2L into 4L, 3 3 3 0


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 7:55 pm 
Offline

Joined: Fri Nov 17, 2006 8:54 pm
Posts: 1770
Location: caversham
Not a full answer but a fudge.

Pour the full 9 fully into the 7. So 9 has two litres and 7 has seven litres.

Pour the 7 fully into the 4. So 7 has three and 4 has four litres.

Pour the 4 into the 2. So 4 and 2 both have two litres.

Now comes the fudge pour half of the 2 into the 9 makes three litres and pour the other half into the 4 makes three litres.

Drawing a diagram helps and if I had more time and patience maybe with a few more steps I could do it without a fudge. :lol:


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 8:05 pm 
Offline

Joined: Wed Jan 11, 2006 7:10 pm
Posts: 8208
Location: Buckinghamshire
My DSs' maths teacher used to revel in setting problems like this.

We quite enjoyed solving them, but when it all got too much it was always "Google Is Your Friend". There is a useful visual representation of how to solve the problem here, http://nrich.maths.org/1977/solution . It confuses things a bit by talking about jugs of 8 litres, but otherwise it seems fairly clear.

But anyway, as far as I can see, minesateas' DS has cracked it as well. Take a gold star, that boy! :D


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 8:09 pm 
Offline

Joined: Mon Aug 22, 2011 8:20 pm
Posts: 1706
Location: Warwickshire
Code:
step                                                                                        9litre       7litre       4litre       2litre
1   fill the 4 litre jug from the 9 litre jug                                                5            0            4            0
2   empty the 4 litre jug into the 7 litre jug                                               5            4            0            0
3   fill the 4 litre jug from the 9 litre jug                                                1            4            4            0
4   fill the 7 litre jug using 3 litres from the 4 litre jug                                 1            7            1            0
5   empty the remaining 1 litre in the 4 litre jug into the 2 litre jug                      1            7            0            1
6   fill the 4 litre jug from the 7 litre jug                                                1            3            4            1
7   fill the 2 litre jug using 1 litre from the 4 litre jug                                  1            3            3            2
8   empty the 2 litre jug into the 9 litre jug                                               3            3            3            0


There may be quicker ways!


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 8:34 pm 
Offline

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 165
Wow, I knew there would be lovely clever people on here.

Perhaps this homework has been set for my 9 year old to find out how intelligent the parents are as we clearly had to help. In my case a dismal fail...

Thank you so much !


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 8:39 pm 
Offline

Joined: Sun May 09, 2010 12:04 pm
Posts: 2615
logic32 wrote:
There are 4 jugs, one is a 9 litre ,then a 7 litre, a 4 litre and a 2 litre .
The 9 litre jug is full, the others are empty. We have to work out how to get 3 litres into 3 of the jugs.


Okanagan wrote:
Code:
step                                                                                        9litre       7litre       4litre       2litre
1   fill the 4 litre jug from the 9 litre jug                                                5            0            4            0
2   empty the 4 litre jug into the 7 litre jug                                               5            4            0            0
3   fill the 4 litre jug from the 9 litre jug                                                1            4            4            0
4   fill the 7 litre jug using 3 litres from the 4 litre jug                                 1            7            1            0
5   empty the remaining 1 litre in the 4 litre jug into the 2 litre jug                      1            7            0            1
6   fill the 4 litre jug from the 7 litre jug                                                1            3            4            1
7   fill the 2 litre jug using 1 litre from the 4 litre jug                                  1            3            3            2
8   empty the 2 litre jug into the 9 litre jug                                               3            3            3            0


There may be quicker ways!


Is there something missing in the question, some conditions about how the water is poured?

I have seen the link on nrich given by Sally-Anne and seen the brilliant work done by Mineatea’s DS (thousands bravos!), but why can’t we just leave aside the smallest jug holding just two litres as it will never hold 3 litres… And then we just pour from the largest jug 3l in second jug (which could hold 7l) and third jug (which could hold 4l) and then it’s job done as three jug contains three litres.
Why to go into complicated stuff?
I know… my reasoning is completely babyish :oops: :cry: … but I just can’t see why we couldn’t do that… Maybe I just need a goodnight sleep!! :lol: :lol:


Top
 Profile  
 
PostPosted: Sun Nov 25, 2012 8:46 pm 
Offline

Joined: Mon Aug 22, 2011 8:20 pm
Posts: 1706
Location: Warwickshire
The trick is to realise that you need to end up with 3 odd numbers. So 9 -(4*2) =1, (4*2)-7=1. Once you've got 1, 1 and 7 it's not too difficult to use the 2 litre jug to move it around in multiples of 2. A slightly easier to follow version with the same number of steps.
Code:
step                                                                                        9litre       7litre       4litre       2litre
1   fill the 4 litre jug from the 9 litre jug                                                5            0            4            0
2   empty the 4 litre jug into the 7 litre jug                                               5            4            0            0
3   fill the 4 litre jug from the 9 litre jug                                                1            4            4            0
4   fill the 7 litre jug using 3 litres from the 4 litre jug                                 1            7            1            0
5   fill the 2 litre jug from the 7 litre jug                                                1            5            1            2
6   empty the 2 litre jug into the 9 litre jug                                               3            5            1            0
7   fill the 2 litre jug from the 7 litre jug                                                3            3            1            2
8   empty the 2 litre jug into the 4 litre jug                                               3            3            3            0


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 52 posts ]  Go to page 1, 2, 3, 4, 5, 6  Next

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
CALL 020 8204 5060
   
Privacy Policy | Refund Policy | Disclaimer | Copyright © 2004 – 2016