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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]  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]  06 Nov 2016, 13:36
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Expert's post
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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Sandy
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Re: A jar contains 4 marbles: 2 red and 2 white. 2 marbles are [#permalink]  07 Nov 2016, 01:30
Expert's post

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

Thank you
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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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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
[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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