Multiple choice

A bag contains 25 marbles, out of which some are red and some are blue. After taking one blue marble out, the probability of selecting a red marble is 3 8 . What is the probability of selecting a blue marble before taking the blue marble out?

  1. 5 8

  2. 15 27

  3. 16 24

  4. 16 25

  5. 14 30
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let R be red and B be blue. Total = 25. After removing one blue, total = 24. P(Red) = R/24 = 3/8, so R = 9. Blue marbles = 25 - 9 = 16. Probability of blue before removal = 16/25.

AI explanation

After one blue marble is removed, 24 marbles remain in the bag. Since the new probability of selecting a red marble is 3/8, the number of red marbles is 3/8 of 24, which equals 9. This means the original bag contained 15 blue marbles and 25 total marbles; using the classical probability formula, the probability of selecting a blue marble initially was 15 divided by 25, which is 16/25.

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