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

Ans is B
see the pic for solution.

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.

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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