Question

The Smith Trucking Company claims that the average weight of its delivery trucks when fully loaded is 6000 pounds with a standard deviation of 120 pounds. 36 trucks are selected at random and their weights recorded. Within what limits will the average weights of 90% of the 36 trucks lie?

Answer 1

$CI=\mu \plusmn z\frac{\sigma}{\sqrt{n}}$

$Z=1.645$ from z value table $\alpha= (1-0.9)/2$

$CI=6000 \plusmn 1.645 \frac{120}{\sqrt{36}}=6000 \plusmn 32.9$