It is currently Sun Jan 21, 2018 11:09 am

 All times are UTC

 Page 1 of 6 [ 52 posts ] Go to page 1, 2, 3, 4, 5, 6  Next
 Print view Previous topic | Next topic
Author Message

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 177
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 ?

Top

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

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 177
No just year 5 homework. Maths isn't exactly my strong point and despite the name nor is logic !!!

Top

Joined: Fri Oct 30, 2009 11:08 pm
Posts: 1234
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

Joined: Fri Nov 17, 2006 8:54 pm
Posts: 1776
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.

Top

Joined: Wed Jan 11, 2006 7:10 pm
Posts: 8764
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!

Top

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

Joined: Mon Jul 26, 2010 6:05 pm
Posts: 177
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

Joined: Sun May 09, 2010 12:04 pm
Posts: 3753
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 … but I just can’t see why we couldn’t do that… Maybe I just need a goodnight sleep!!

Top

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

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 6 [ 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 forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

Search for:
 Jump to:  Select a forum ------------------ FORUM RULES    Forum Rules and FAQs 11 PLUS SUBJECTS    VERBAL REASONING    MATHS    ENGLISH    NON-VERBAL REASONING    CEM 11 Plus GENERAL    GENERAL 11 PLUS TOPICS    11 PLUS APPEALS    11 PLUS TUTORS    INDEPENDENT SCHOOLS    11 PLUS CDs/SOFTWARE    11 PLUS TIPS    PRIMARY    SEN and the 11 PLUS    EVERYTHING ELSE .... 11 PLUS REGIONS    Berkshire    Bexley and Bromley    Birmingham, Walsall, Wolverhampton and Wrekin    Buckinghamshire    Devon    Dorset    Essex    Essex - Redbridge    Gloucestershire    Hertfordshire (South West)    Hertfordshire (Other and North London)    Kent    Lancashire & Cumbria    Lincolnshire    Medway    Northern Ireland    Surrey (Sutton, Kingston and Wandsworth)    Trafford    Warwickshire    Wiltshire    Wirral    Yorkshire BEYOND 11 PLUS    Beyond 11 Plus - General    GCSEs    6th Form    University