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Intern  B
Joined: 13 Apr 2019
Posts: 28
A bag consists of 56 marbles, each of which is either green, white, or  [#permalink]

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1
1 00:00

Difficulty:   25% (medium)

Question Stats: 82% (01:25) correct 18% (03:02) wrong based on 38 sessions

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A bag consists of 56 marbles, each of which is either green, white, or red. If the probability of selecting a green marble is twice the probability of selecting a red marble, and the probability of selecting a white marble is twice the probability of selecting a green marble, how many red marbles are in the bag?

(A) 7
(B) 8
(C) 14
(D) 16
(E) 28
Senior Manager  P
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Posts: 280
Re: A bag consists of 56 marbles, each of which is either green, white, or  [#permalink]

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Since there are 56 marbles
So, g + w + r = 56
according to question,
g = 2r
w = 2g
we can substitute each of the equations
and solve for g and find g= 16
Now solve for the number of red marbles:
16 = 2r
r =8
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Re: A bag consists of 56 marbles, each of which is either green, white, or  [#permalink]

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Ratio of G:R is 2:1
Ratio of W:G is 4:1

the ratio of R:W:R:Total is 2:4:1:7
if total is 56, so R = 8, which is Answer B
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Re: A bag consists of 56 marbles, each of which is either green, white, or  [#permalink]

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let probability of selecting a red marble be x/56
then probability of selecting a green marble becomes 2x/56
and probability of selecting a white marble will be 4x/56
as we know sum of their prob will be 1
i.e x/56+2x/56+4x/56 = 1
7x/56=1
x=8
so,probability of selecting a red marble is 8
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Re: A bag consists of 56 marbles, each of which is either green, white, or  [#permalink]

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Brant22 wrote:
A bag consists of 56 marbles, each of which is either green, white, or red. If the probability of selecting a green marble is twice the probability of selecting a red marble, and the probability of selecting a white marble is twice the probability of selecting a green marble, how many red marbles are in the bag?

(A) 7
(B) 8
(C) 14
(D) 16
(E) 28

Notice that when the probability of choosing one kind of marble is twice the probability of choosing another kind of marble, it means that the number of marbles with the greater probability is twice the number of the other kind of marble. If we let the number of red marbles = r, then the number of green marbles = 2r and the number of white marbles = 4r.

Thus:

r + 2r + 4r = 56

7r = 56

r = 8

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If you find one of my posts helpful, please take a moment to click on the "Kudos" button. Re: A bag consists of 56 marbles, each of which is either green, white, or   [#permalink] 16 Apr 2019, 17:46
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