In: Statistics and Probability
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
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