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

Question

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

chetan2u · Answer

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

Bunuel · Answer

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

sahilvijay · Answer

Ans is B
see the pic for solution.

pclawong · Answer

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

sahilvijay · Answer

Always stick to fundamentals and go by procedure and you will never go wrong. I hope your doubt is clear.

BrentGMATPrepNow · Answer

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

Answer: B

Cheers,
Brent

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