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Updated on: 26 Nov 2018, 05:07
Originally posted by vigneshpandi on 08 Sep 2010, 20:56.
Last edited by Bunuel on 26 Nov 2018, 05:07, edited 2 times in total.
Last edited by Bunuel on 26 Nov 2018, 05:07, edited 2 times in total.
Edited the question and added the OA.
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
73% (02:49) correct
27%
(02:57)
wrong
based on 1430
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Bag A contains red, white and blue marbles such that the red to white marble ratio is 1:3 and the white to blue marble ratio is 2:3. Bag B contains red and white marbles in the ratio of 1:4. Together, the two bags contain 30 white marbles. How many red marbles could be in bag A?
A. 1
B. 3
C. 4
D. 6
E. 8
Explanation:
A. 1
B. 3
C. 4
D. 6
E. 8
Explanation:
We are told that bag B contains red and white marbles in the ration 1:4. This implies that WB, the number of white marbles in bag B, must be a multiple of 4.
What can we say about WA, the number of white marbles in bag A? We are given two ratios involving the white marbles in bag A. The fact that the ratio of red to white marbles in bag A is 1:3 implies that WA must be a multiple of 3. The fact that the ratio of white to blue marbles in bag A is 2:3 implies that WA must be a multiple of 2. Since WA is both a multiple of 2 and a multiple of 3, it must be a multiple of 6.
We are told that WA + WB = 30. We have already figured out that WA must be a multiple of 6 and that WB must be a multiple of 4. So all we need to do now is to test each candidate value of WA (i.e. 6, 12, 18, and 24) to see whether, when plugged into WA + WB = 30, it yields a value for WB that is a multiple of 4. It turns out that WA = 6 and WA = 18 are the only values that meet this criterion.
Recall that the ratio of red to white marbles in bag A is 1:3. If there are 6 white marbles in bag A, there are 2 red marbles. If there are 18 white marbles in bag A, there are 6 red marbles. Thus, the number of red marbles in bag A is either 2 or 6. Only one answer choice matches either of these numbers.
The correct answer is D.
What can we say about WA, the number of white marbles in bag A? We are given two ratios involving the white marbles in bag A. The fact that the ratio of red to white marbles in bag A is 1:3 implies that WA must be a multiple of 3. The fact that the ratio of white to blue marbles in bag A is 2:3 implies that WA must be a multiple of 2. Since WA is both a multiple of 2 and a multiple of 3, it must be a multiple of 6.
We are told that WA + WB = 30. We have already figured out that WA must be a multiple of 6 and that WB must be a multiple of 4. So all we need to do now is to test each candidate value of WA (i.e. 6, 12, 18, and 24) to see whether, when plugged into WA + WB = 30, it yields a value for WB that is a multiple of 4. It turns out that WA = 6 and WA = 18 are the only values that meet this criterion.
Recall that the ratio of red to white marbles in bag A is 1:3. If there are 6 white marbles in bag A, there are 2 red marbles. If there are 18 white marbles in bag A, there are 6 red marbles. Thus, the number of red marbles in bag A is either 2 or 6. Only one answer choice matches either of these numbers.
The correct answer is D.
08 Sep 2010, 21:27
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vigneshpandi
Bag A:
R/W=1/3=2/6;
W/B=2/3=6/9;
So R/W/B=2/6/9 --> # of marbles in bag A would be \(2x\), \(6x\), and \(9x\), for some positive integer multiple \(x\), where \(6x\) corresponds to the # of white marbles and \(2x\) corresponds to the # of red marbles (so # of red marbles must be a multiple of 2, so answers A and B are out at this stage);
Bag B:
R/W=1/4 --> # of marbles in bag B would be \(y\) and \(4y\), for some positive integer multiple \(y\), where \(4y\) corresponds to the # of white marbles;
Given: \(6x+4y=30\) --> \(3x+2y=15\) --> there are two positive integer solutions for this equation:
\(x=3\) and \(y=3\) --> in this case # of red marbles equals to \(2x=6\);
Or:
\(x=1\) and \(y=6\) --> in this case # of red marbles equals to \(2x=2\);
Only 6 is in the answer choices.
Answer: D.
10 Nov 2011, 23:01
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enigma123
Responding to a pm:
We need the relation between number of red, white and total number of marbles.
We don't know what that relation in bag A. Let's find it out first.
Red:White = 1:3 = 2:6
White:Blue = 2:3 = 6:9
Red:White:Blue = 2:6:9
In bag A, if you have 17 marbles, 2 will be Red, 6 will be White and 9 will be Blue.
If you have 34 marbles, 4 will be Red, 12 will be White and 18 will be Blue etc
No of white marbles could be 6/12/18/24... etc
No of red marbles could be 2/4/6/8/... etc
In bag B,
Red:White = 1:4
If you have 5 marbles, 1 will be Red, 4 will be White.
If you have 10 marbles, 2 will be Red, 8 will be White.
etc
No of white marbles could be 4/8/12/16... etc
No of red marbles could be 1/2/3/4... etc
Total number of white marbles = 30
There are two ways in which we could have obtained 30.
White marbles in (Bag A, Bag B) = (6, 24) or (18, 12)
If Bag A has 6 white marbles, it will have 2 red marbles.
If Bag A has 18 white marbles, it will have 6 red marbles.
Answer (D).
