Question

On average a University Book Shop sells 300 text books per day with a standard deviation of 50 text books. Find the probability that the University Book Shop will sell at least 400 text books per day

Answer 1

Solution:

Given, $\mu=300,\sigma=50$

$X\sim N(\mu,\sigma) \\P(X\ge400)=1-P(X<400) \\=1-P(z<\dfrac{400-300}{50}) \\=1-P(z<2) \\=1-0.97725 \\=0.02275$