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A jar contains 4 marbles: 2 red and 2 white. 2 marbles are

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A jar contains 4 marbles: 2 red and 2 white. 2 marbles are [#permalink] New post 06 Nov 2016, 13:06
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A jar contains 4 marbles: 2 red and 2 white. 2 marbles are chosen at random.

Quantity A
Quantity B
The probability that the marbles chosen are the same colour
The probability that the marbles chosen are different colours.



A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

Last edited by Carcass on 07 Nov 2016, 01:29, edited 1 time in total.
Edited by Carcass
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Re: A jar contains 4 marbles: 2 red and 2 white. 2 marbles are [#permalink] New post 06 Nov 2016, 13:36
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Here,

Quantity A:

P(The probability that the marbles chosen are the same color)= P(RED)*P(RED)+P(BLUE)*P(BLUE) = \(\frac{2}{4}*\frac{1}{3} + \frac{2}{4}*\frac{1}{3}\)

= \(\frac{1}{3}\)

Quantity B:

P(The probability that the marbles chosen are different colours) = P(RED)*P(BLUE)+P(BLUE)*P(RED)
=\(\frac{2}{4}*\frac{2}{3}+\frac{2}{4}*\frac{2}{3}\)
=\(\frac{2}{3}\)

Hence Quantity B is greater.
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Re: A jar contains 4 marbles: 2 red and 2 white. 2 marbles are [#permalink] New post 07 Nov 2016, 01:30
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Please follow the rules how to post a question

qq-how-to-post-a-gre-question-the-easy-way-2357.html

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Re: A jar contains 4 marbles: 2 red and 2 white. 2 marbles are [#permalink] New post 13 Nov 2016, 07:30
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SJ wrote:
A jar contains 4 marbles: 2 red and 2 white. 2 marbles are chosen at random.

Quantity A
Quantity B
The probability that the marbles chosen are the same colour
The probability that the marbles chosen are different colours.




Here's a quick approach.

First pick 1 marble, ANY marble. For this first step, picking either color is equally likely.
At this point, there are 3 marbles remaining in the jar. 1 marble is the SAME color as the first marble you selected, and 2 marbles are a DIFFERENT color from the first marble you selected.
So, it's more likely that the two marbles will be DIFFERENT colors
Answer:
[Reveal] Spoiler:
B


Mathematically, P(matching colors) = 1/3 and P(different colors) = 2/3
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Re: A jar contains 4 marbles: 2 red and 2 white. 2 marbles are   [#permalink] 13 Nov 2016, 07:30
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