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A jar contains 20 marbles: 4 red, 6 white and 10 blue
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06 Nov 2016, 13:11
06 Nov 2016, 13:11
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Question Stats:
41% (01:00) correct
58% (01:11) wrong based on 39 sessions
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A jar contains 20 marbles: 4 red, 6 white and 10 blue. If you remove marbles one at a time, randomly, what is the minimum number that must be removed to be certain that you have at least 2 marbles of each colour?
A. 6
B. 10
C. 12
D. 16
E. 18
A. 6
B. 10
C. 12
D. 16
E. 18
Re: A jar contains 20 marbles: 4 red, 6 white and 10 blue
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22 Aug 2018, 15:51
22 Aug 2018, 15:51
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Expert Reply
anabanana wrote:
what I don't understand is why this must be a worst case scenario. the question asks for the minimum number that must be removed -- doesn't that mean best case scenario? In which case, wouldn't the answer be 4 red+6 white+2 blue = 12?
The key is in the language of the question: 'the minimum number of marbles removed so that you are certain', certain being the keyword here. Now you can remove the 12 marbles as you pointed out but can you be certain that you have each kind.
Say you pick twelve: 10 blue and 2 white. Hence no red at in the selection. Hence we assume the worst case scenario.
General Discussion
Re: A jar contains 20 marbles: 4 red, 6 white and 10 blue
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06 Nov 2016, 13:40
06 Nov 2016, 13:40
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Expert Reply
Here we have 10 Blue 6 White and 4 Red. The worst case scenario you pull all white and blue before you pull 2 red.
Hence minimum number of marbles you need the pull is all 10 white, 6 White and 2 Red.
Number of marbles to be removed = \(10 + 6 + 2\) = \(18\)
Hence minimum number of marbles you need the pull is all 10 white, 6 White and 2 Red.
Number of marbles to be removed = \(10 + 6 + 2\) = \(18\)
