Question

Electricity bills in a certain city have mean $ 84.26 . Assume the bills are normally distributed with standard deviation $ 16.60 . Find the value that separates the lower 63 % of the bills from the rest. Write only a number as your answer. Round to two decimal places (for example: 42.81). Do not write any units.

Answer 1

We are given,

let x be the electricity bill in a certain city.

x follow normal distribution with mean $ 84.26 and standard deviation $16.60

We are asked to find x such that area below x is 63%

We can use TI-84 calculator to find such x.

Press 2ND key ----> VARS key ---> scroll to invNorm() and hit enter.

Then plug the given values accordingly,

Scroll to paste and hit enter two times

Answer : 89.77