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Retired Moderator V
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There are two boxes A and B. In box A, there are 3 red marbles and  [#permalink]

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Difficulty:   25% (medium)

Question Stats: 79% (02:23) correct 21% (02:35) wrong based on 179 sessions

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There are two boxes A and B. In box A, there are 3 red marbles and 5 green marbles. In box B, there are 2 red marbles and 3 green marbles. Jack rolls the dice. If the result is 1 or 6 then Jack will pick a marble from box A. If the result is neither 1 nor 6 then Jack will pick a marble from box B. What is the probability that the picked marble is green?

A. 1/8
B. 73/120
C. 21/40
D. 5/24
E. 25/56

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Senior Manager  B
Joined: 13 Oct 2016
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There are two boxes A and B. In box A, there are 3 red marbles and  [#permalink]

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3
Hi again Events are independent hence:

$$P(A)*P(Green) + P(B)*P(Green)$$

$$\frac{2}{6} * \frac{5}{8} + \frac{4}{6}* \frac{3}{5} = \frac{146}{6*40} = \frac{73}{120}$$

Answer B.
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Re: There are two boxes A and B. In box A, there are 3 red marbles and  [#permalink]

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nguyendinhtuong wrote:
There are two boxes A and B. In box A, there are 3 red marbles and 5 green marbles. In box B, there are 2 red marbles and 3 green marbles. Jack rolls the dice. If the result is 1 or 6 then Jack will pick a marble from box A. If the result is neither 1 nor 6 then Jack will pick a marble from box B. What is the probability that the picked marble is green?

A. 1/8
B. 73/120
C. 21/40
D. 5/24
E. 25/56

We are given that in box A, there are 3 red marbles and 5 green marbles, and in box B, there are 2 red marbles and 3 green marbles. When the die is rolled, if the result is 1 or 6 then Jack will pick a marble from box A, and if the result if neither 1 nor 6 then Jack will pick a marble from box B. We need to determine the probability that a green marble is selected.

Notice that the probability that a green marble is selected is the probability that a green marble is selected from box A or from box B. That is, the probability of selecting a green marble is the probability that it’s selected from box A plus the probability that it’s selected from box B. Let’s start with box A.

P(rolling a 1 or 6) = 2/6 = 1/3

P(selecting a green marble) = 5/8

Thus, the probability of selecting a green marble from box A is 1/3 x 5/8 = 5/24.

Now we can move to box B.

P(not rolling a 1 or 6) = 2/3

P(selecting a green marble) = 3/5

Thus, the probability of selecting a green marble from box B is 2/3 x 3/5 = 2/5.

The probability of selecting a green marble from box A or box B is:

5/24 + 2/5 = 25/120 + 48/120 = 73/120

Answer: B
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Intern  B
Joined: 30 Nov 2018
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GMAT 1: 350 Q27 V12 There are two boxes A and B. In box A, there are 3 red marbles and  [#permalink]

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Can anyone please explain how the probability of getting green marble in the second condition is 3/5?
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Joined: 07 Sep 2017
Posts: 6
Re: There are two boxes A and B. In box A, there are 3 red marbles and  [#permalink]

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Balakumaran19 wrote:
Can anyone please explain how the probability of getting green marble in the second condition is 3/5?

The total number of marbles in Box B is 5 (2 Red and 3 Green). Therefore the probability of green marble is Green marble/Total marbles in Box B which is 3/5. Hope this helps! Re: There are two boxes A and B. In box A, there are 3 red marbles and   [#permalink] 15 Feb 2019, 10:56
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