Question

In earlier days, there was a chance to make a telephone call would be of 0.6. Determine the probability when it could make 11 successes in 20 attempts of phone call.

(a) 0.2783

(b) 0.2013

(c) 0.1597

(d) 3.8561

I had been asked this question during an interview.

Question is taken from Counting in division Counting of Discrete Mathematics

Answer 1

Right choice is (c) 0.1597

The best I can explain: Probability of success p=0.6 and q=0.4. X=success in making a telephone call. Hence, the probability of 11 successes in 20 attempts = P(X=11) = ^20C11(0.6)^11(0.4)^20 – 11 = 0.1597.