Multiple choice

A box contains 4 white balls and 3 red balls. In succession, two balls are randomly selected and removed from the box. Given that the first removed ball is white, the probability that the second removed ball is red is

  1. 1/3

  2. 3/7

  3. 1/2

  4. 4/7
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Initial: 4 white, 3 red. After removing 1 white: 3 white, 3 red remain. Probability of picking red = 3 / (3+3) = 3/6 = 1/2.

AI explanation

Because the first removed ball is known to be white, we use conditional probability to evaluate the second draw from the remaining balls. After removing one white ball, the box now contains 3 white balls and 3 red balls, giving a total of 6 balls. The probability that the second removed ball is red is the number of red balls divided by the new total, which is 3 divided by 6, yielding 1/2.

Keep practicing — related questions