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# A certain jar contains 21 marbles, 7 of which are red. If two marbles

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Math Expert
Joined: 02 Sep 2009
Posts: 53063
A certain jar contains 21 marbles, 7 of which are red. If two marbles  [#permalink]

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17 Jan 2019, 23:50
00:00

Difficulty:

15% (low)

Question Stats:

95% (00:45) correct 5% (00:39) wrong based on 23 sessions

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A certain jar contains 21 marbles, 7 of which are red. If two marbles are to be selected, with replacement, what is the probability that both marbles will be red?

A 1/9
B 1/6
C 1/3
D 2/3
E 3/4

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Intern
Joined: 05 Jan 2018
Posts: 7
Re: A certain jar contains 21 marbles, 7 of which are red. If two marbles  [#permalink]

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18 Jan 2019, 03:52
A certain jar contains 21 marbles, 7 of which are red. If two marbles are to be selected, with replacement, what is the probability that both marbles will be red?

No. of ways of selecting 2 red marbles = 7* 7
No. of way of selecting any 2 marbles = 21*21
Probability of selecting 2 marbles = 7*7/21*21 = 1/9

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Joined: 18 Aug 2017
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Location: India
Concentration: Sustainability, Marketing
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WE: Marketing (Energy and Utilities)
Re: A certain jar contains 21 marbles, 7 of which are red. If two marbles  [#permalink]

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18 Jan 2019, 06:19
Bunuel wrote:
A certain jar contains 21 marbles, 7 of which are red. If two marbles are to be selected, with replacement, what is the probability that both marbles will be red?

A 1/9
B 1/6
C 1/3
D 2/3
E 3/4

7/21 * 7/21 = 1/9
IMO A
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Re: A certain jar contains 21 marbles, 7 of which are red. If two marbles   [#permalink] 18 Jan 2019, 06:19
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