Chapter 7 - Section 7.3 - Shape of the Sampling Distribution of x - Exercises - Page 289: 7.27

$\mu$= 168 minutes, σ = 20 minutes, n = 400 When n=400 $\mu$ = $\mu$ _${\bar{x}}$= 168 σ_${\bar{x}\ }$ = $\frac{σ}{\sqrt n}$ = $\frac{20}{\sqrt 400 }$ = 1 minute The sampling distribution of $\bar{x}\ $ when n=400 is approximately normally distributed. We do not need to know the shape of the population distribution in order to make this conclusion, because the sampling distribution is normally distributed when s = 1.

--