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karan12345
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An urn contains some red balls, 5 blue balls and 3 green balls. Two 25 May 2020, 09:57
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45% (medium)

Question Stats:

78% (01:20) correct 22% (01:20) wrong based on 9 sessions

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An urn contains some red balls, 5 blue balls and 3 green balls. Two balls are drawn, one by one, with replacement. Find the probability that fifth ball is red.

(1) Number of red balls are 8 less than the total number of balls.
(2) Total number of balls are 16.

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chetan2u
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An urn contains some red balls, 5 blue balls and 3 green balls. Two 27 May 2020, 00:29
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karan12345
An urn contains some red balls, 5 blue balls and 3 green balls. Two balls are drawn, one by one, with replacement. Find the probability that fifth ball is red.

(1) Number of red balls are 8 less than the total number of balls.
(2) Total number of balls are 16.
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So we have R red balls, 5 blue and 3green balls => R+5+3=R+8.
To know the probability that the fifth ball is Red, we require to know R.

(1) Number of red balls are 8 less than the total number of balls.
We already know this, Total = R+8, or R=Total-8.

(2) Total number of balls are 16
Now Total = 16, so R=16-8=8.
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B
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An urn contains some red balls, 5 blue balls and 3 green balls. Two 27 May 2020, 01:14
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chetan2u
karan12345
An urn contains some red balls, 5 blue balls and 3 green balls. Two balls are drawn, one by one, with replacement. Find the probability that fifth ball is red.

(1) Number of red balls are 8 less than the total number of balls.
(2) Total number of balls are 16.


So we have R red balls, 5 blue and 3green balls => R+5+3=R+8.
To know the probability that the fifth ball is Red, we require to know R.

(1) Number of red balls are 8 less than the total number of balls.
We already know this, Total = R+8, or R=Total-8.

(2) Total number of balls are 16
Now Total = 16, so R=16-8=8.
Suff

B
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Hi chetan,

I was able to solve this, but would like to understand the logic for calculating probability here.
Since, we are replacing each ball, so the probability of 5th pick being a red ball will be the same as the first pick being a red ball.

Kindly, correct me if the above reasoning is wrong.

Thanks
Lipun
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An urn contains some red balls, 5 blue balls and 3 green balls. Two 27 May 2020, 10:01
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Lipun

I was able to solve this, but would like to understand the logic for calculating probability here.
Since, we are replacing each ball, so the probability of 5th pick being a red ball will be the same as the first pick being a red ball.
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You ask a very good question - the problem reads:

Quote:

An urn contains some red balls, 5 blue balls and 3 green balls. Two balls are drawn, one by one, with replacement. Find the probability that fifth ball is red.
Show more

I have no clue what the question even means - if we're only picking two balls, there is no "fifth ball" at all. As written the question makes no sense.

Chetan correctly answered the question "how many red balls are there", which is presumably going to be sufficient to answer whatever the question was attempting to ask. Statement 1 tells us 8 balls are not red (something we already knew), and Statement 2 tells us 8 balls are red, so the answer to that question is B.

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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
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