Question

How to solve using functions in TI84:

In order to set rates, an insurance company is trying to estimate the number of sick days that full time workers at an auto repair shop take per year. A previous study indicated that the standard deviation was 2.8 days. How large a sample must be selected if the company wants to be 95% confident that the true mean differs from the sample mean by no more than 1 day?

A)141 B)31 C)1024 D)512

Answer 1

Solution:

Given ,

= 2.8 ..Population SD

E = 1 Margin of error

c= 95% =0.95 ...confidence level

= 1- c = 1- 0.95 = 0.05

  /2 = 0.025

1- /2 = 0.975

Find sample size required.

Frmula for sample size is

Use TI 84 calculator.

Press 2nd and then press VARS.

Go to invNorm(

invNorm(0.975 , 0 , 1)

= 1.95996398454

Then ,

1.95996398454 * 2.8 = 5.48789915671

5.48789915671/1 = 5.48789915671

(5.48789915671)² = 30.1170371542

= 31

Answer is 31