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PostPosted: Sat Oct 19, 2013 9:01 am 
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The ratio of purple to yellow marbles in a bag is 5:6
The next day I add 28 more marbles to the bag. Now the ratio is 1:2 of purple to yellow.
How many purple marbles did we have at the beginning and at the end and how many total marbles do we have ?

Many thanks !
Queenma


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PostPosted: Sat Oct 19, 2013 9:10 am 
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What colour are the ones you are adding? All yellow? Or a mixture?


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PostPosted: Sat Oct 19, 2013 9:11 am 
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I am not sure that there is enough info in this...


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PostPosted: Sat Oct 19, 2013 11:13 am 
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Given, Purple: Yellow as 5:6, assume there are a total of 11 marbles in the beginning
Adding 28 marbles more, will give a number of 11+28= 39
Now the new ratio of purple to yellow is 1:2
So, 39/(1+2) ie. 39/3=13
13 purple and 26 yellow at the end in the bag.

So, in the new lot of added 28 marbles, there had been 8 purple and 20 yellow.
Beginning - 5 purple marbles
End- 13 purple marbles.

I guess so, :o


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PostPosted: Sat Oct 19, 2013 12:24 pm 
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I worked it out exactly as Rejim2! Would be interested to have confirmation - or otherwise - that this is correct! :D

Where did you get the question from, Queenma?

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PostPosted: Sat Oct 19, 2013 12:54 pm 
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Thanks rejim2 and fatbananas.
This was from a paper of an independent school - Channing I think.
My daughter got the same answer ! I wanted to confirm it - because I thought there could be more than one answer here !

Queenma.


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PostPosted: Sat Oct 19, 2013 1:45 pm 
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If it doesn't say which colour you add, there's more than one answer.

The scenario suggested above certainly works.

But there's also e.g.

Original ratio is 5:6
Final ratio is 1:2 which is equivalent to 5:10
Therefore 4 'parts' of yellow marbles have been added.
Therefore 1 'part' of yellow marbles = 7
Therefore you started off with 35 purple and 42 yellow, added 28 yellow to get 35 purple and 70 yellow, i.e. 105 altogether.

Or:
Start off with 20 purple and 24 yellow.
Add 4 purple and 24 yellow to give 24 purple and 48 yellow.

Think those are the only 3 possibilities. Was this a multiple choice question? If there was only one choice of answer that worked, I suppose that's ok :) But otherwise you have to make assumptions, which isn't ok.


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PostPosted: Sat Oct 19, 2013 2:50 pm 
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Joined: Tue Jul 21, 2009 9:56 pm
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QUEENMA wrote:
The ratio of purple to yellow marbles in a bag is 5:6
The next day I add 28 more marbles to the bag. Now the ratio is 1:2 of purple to yellow.
How many purple marbles did we have at the beginning and at the end and how many total marbles do we have ?

Many thanks !
Queenma


Did you copy out this question exactly? The language is a little odd for a maths problem in a test paper.


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