Multiple choice

A bag contains 5 white and 3 black balls. 4 balls are successively drawn out of the bag and are not replaced. What is the chance of getting different colours alternatively?

  1. 1/6

  2. 1/5

  3. 1/4

  4. 1/7

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total balls = 8. Drawing 4 balls without replacement. To get different colors alternatively, the sequences must be W-B-W-B or B-W-B-W. Probability of W-B-W-B = (5/8)(3/7)(4/6)(2/5) = 120/1680 = 1/14. Probability of B-W-B-W = (3/8)(5/7)(2/6)(4/5) = 120/1680 = 1/14. Total probability = 1/14 + 1/14 = 2/14 = 1/7.