BTGmoderatorLU wrote: ↑Fri Feb 26, 2021 5:35 pm
Source: Official Guide
A box contains only red chips, white chips, and blue chips. If a chip is randomly selected from the box, what is the probability that the chip will be either white or blue?
1) The probability that the chip will be blue is 1/5
2) The probability that the chip will be red is 1/3
The OA is
B
Target question: What is the probability that the chip is either white or blue?
Given: The box contains only red chips, white chips, and blue chips
Statement 1: The probability that the chip will be blue is 1/5.
This tells us that 1/5 of the chips are BLUE, but there's no information about the WHITE chips.
Consider these two possible cases:
Case a: There are 5 chips in total. 1 chip is blue, and 1 chip is white. In this case, the answer to the target question is
P(chip is either white or blue) = 2/5
Case b: There are 5 chips in total. 1 chip is blue, and 2 chips are white. In this case, the answer to the target question is
P(chip is either white or blue) = 3/5
Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: The probability that the chip will be red is 1/3
This also tells us that
the probability of selecting a NON-RED chip is 2/3
Since the box contains only red chips, white chips, and blue chips, then selecting a NON-RED chip is the same as selecting either a BLUE chip OR a WHITE chip
In other other words, P(select NON-BLUE chip) = P(selecting either a BLUE chip OR a WHITE chip)
So, the answer to the target question is
P(chip is either white or blue) = 2/3
Answer: B
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
