Answer to Question #191505 in Statistics and Probability for beep beep

Question

Given there is 0.85 probability that any given adult knows Twitter, find the probability of getting four adults who know of Twitter when seven adults are randomly selected.

Answer 1

$p=0.85 \\ q = 0.15 \\ n = 7 \\ P(X=4) = C^7_4 (0.85)^4(0.15)^{7-4} \\ = \frac{7!}{4!(7-4)!} \times 0.522 \times 0.003375 \\ = 0.0616$

Answer: 0.0616