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