[email protected] wrote:Certain bowl contains 5 red marbles and 3 blue marbles only. One by one, every marble is drawn at random and without replacement. What is the probability that the seventh marble drawn is NOT blue?
In other words, what is the probability that the seventh marble selected is red?
No math is needed here if we understand the following concept:
The probability of selecting X on the NTH pick is equal to the probability of selecting X on the FIRST pick.
Thus, P(red on the 7th pick) = P(red on the first pick) = 5/8.
The answer would be the same even if the problem were as follows:
A certain bowl contains 5 red marbles and 3 blue marbles only. One by one, every marble is drawn at random and without replacement. What is the probability that the FIFTH marble drawn is NOT blue?
P(red on the 5th pick) = P(red on the 1st pick) = 5/8.
Other problems that test the same concept:
https://www.beatthegmat.com/probablity-ques-t60161.html
https://www.beatthegmat.com/manhattan-pr ... 89481.html (2 posts)
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