Question

Assume that when adults with smartphones are randomly​ selected, 61​% use them in meetings or classes. If 7 adult smartphone users are randomly​ selected, find the probability that exactly 3 of them use their smartphones in meetings or classes.

Answer 1

p = 61 % = 0.61

n = 7

$P(X=x) = \frac{n!}{x!(n-x)!} \times p^x \times (1-p)^{n-x} \\ p(X=3) = \frac{7!}{3!(7-3)!} \times 0.61^3 \times (1-0.61)^{7-3} \\ = 42 \times 0.61^3 \times 0.39^4 \\ = 0.160$