Question

A bag contains 4 red and 7 blue balls. What is the probability of drawing a blue ball if the first ball drawn is red? The balls drawn are replaced into the bag.

(a) \(\frac {8}{11}\)

(b) \(\frac {7}{11}\)

(c) \(\frac {4}{11}\)

(d) \(\frac {7}{4}\)

I got this question in a job interview.

I'd like to ask this question from Multiplication Theorem on Probability in portion Probability of Mathematics – Class 12

Answer 1

Correct answer is (b) \(\frac {7}{11}\)

The explanation is: Total number of balls = 4 + 7 = 11

The probability of the first ball to be red = \(\frac {4}{11}\)

The probability of drawing blue ball as the second ball out with replacement = \(\frac {7}{11}\)