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# A box contains only red chips, green chips and blue chips. If a chip i

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A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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27 Aug 2017, 19:51
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Difficulty:

25% (medium)

Question Stats:

70% (00:44) correct 30% (00:51) wrong based on 119 sessions

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A box contains only red chips, green chips and blue chips. If a chip is randomly selected from the box, what is the probability that the chip is either red or green?

A. The probability of selecting green chip is 1/3

B. The Probability of selecting a blue chip is 1/7

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Chasing the dragon
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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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27 Aug 2017, 20:26
1
fitzpratik wrote:
A box contains only red chips, green chips and blue chips. If a chip is randomly selected from the box, what is the probability that the chip is either red or green?

A. The probability of selecting green chip is 1/3

B. The Probability of selecting a blue chip is 1/7

hi..

I am sure these type of Qs would have been discussed in various ways in the forum..

in such Qs main point is to remember: - 3 things probability that it is 3rd item is equal to probability it is not the FIRST two AND vice-versa..

either red or green..
1) we require to know each of red and green
2) OR we require to know about blue

A. The probability of selecting green chip is 1/3
we require to know red too..
insuff

B. The Probability of selecting a blue chip is 1/7
sufficient ans 1-1/7=6/7

B
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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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28 Aug 2017, 02:14
chetan2u wrote:
fitzpratik wrote:
A box contains only red chips, green chips and blue chips. If a chip is randomly selected from the box, what is the probability that the chip is either red or green?

A. The probability of selecting green chip is 1/3

B. The Probability of selecting a blue chip is 1/7

hi..

I am sure these type of Qs would have been discussed in various ways in the forum..

in such Qs main point is to remember: - 3 things probability that it is 3rd item is equal to probability it is not the FIRST two AND vice-versa..

either red or green..
1) we require to know each of red and green
2) OR we require to know about blue

A. The probability of selecting green chip is 1/3
we require to know red too..
insuff

B. The Probability of selecting a blue chip is 1/7
sufficient ans 1-1/7=6/7

B

Yes, this is a copy of the following OG question: https://gmatclub.com/forum/a-box-contai ... 44131.html

Similar question from Magoosh: https://gmatclub.com/forum/a-box-contai ... 95322.html
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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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28 Aug 2017, 02:44
Ans is B
see the pic for solution.
Attachments

IMG_5248.JPG [ 2.43 MiB | Viewed 1655 times ]

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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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28 Aug 2017, 20:02
good question, i fall into a little trap
i thought we need to get the % of red
but actually we just need to subtract the blue portion then we can get green and red
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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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28 Aug 2017, 23:01
pclawong wrote:
good question, i fall into a little trap
i thought we need to get the % of red
but actually we just need to subtract the blue portion then we can get green and red

Always stick to fundamentals and go by procedure and you will never go wrong. I hope your doubt is clear.
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Re: A box contains only red chips, green chips and blue chips. If a chip i  [#permalink]

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12 Aug 2018, 06:05
Top Contributor
fitzpratik wrote:
A box contains only red chips, green chips and blue chips. If a chip is randomly selected from the box, what is the probability that the chip is either red or green?

A. The probability of selecting green chip is 1/3

B. The Probability of selecting a blue chip is 1/7

Target question: What is the probability that the chip is either red or green?

Given: The box contains only red chips, green chips and blue chips

Statement 1: The probability of selecting green chip is 1/3
This tells us that 1/3 of the chips are GREEN, but there's no information about the RED chips.

Consider these two possible cases:
Case a: There are 6 chips in total. 2 chips are green, and 2 chips are red. In this case, the answer to the target question is P(chip is red or green) = 4/6
Case b: There are 6 chips in total. 2 chips are green, and 3 chips are red. In this case, the answer to the target question is P(chip is red or green) = 5/6
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: The probability of selecting a blue chip is 1/7
This also tells us that the probability of selecting a NON-BLUE chip is 6/7
Since the box contains only red chips, green chips and blue chips, then selecting a NON-BLUE chip is the same as selecting either a RED chip OR a green chip
In other other words, P(select NON-BLUE chip) = P(selecting either a RED chip OR a green chip)
So, the answer to the target question is P(chip is red or green) = 6/7

Cheers,
Brent
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Re: A box contains only red chips, green chips and blue chips. If a chip i   [#permalink] 12 Aug 2018, 06:05
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