Question

Assume that when adults with smartphones are randomly​ selected, ​64% use them in meetings or classes. If 9 adult smartphone users are randomly​ selected, find the probability that exactly 2 of them use their smartphones in meetings or classes.

Answer 1

Solution:

$p = 64 \% = 0.64$

n = 9

$X\sim Bin(n,p)$

$P(X=x) = \frac{n!}{x!(n-x)!} \times p^x \times (1-p)^{n-x} \\ P(X=2) = \frac{9!}{2!(9-2)!} \times 0.64^2 \times (1-0.64)^{9-2} \\ = 0.01155$