Question

14. A cellular telephone company recently conducted research into the length of calls (in

minutes) made by customers. In a random sample of 30 calls, the sample mean was
x= 18.6 minutes and the standard deviation was s=5.2 minutes. Construct and interpret
a 90% confidence interval for true mean call length. (4-step process)

Answer 1

The correct answer is "16.987, 20213".

Explanation:

Given that,

`n=30`

`\bar x=18.6`

`s = 5.2`

`df=30-1`

`=29`

`\alpha = 0.10`

By using the table, the critical values of t will be:

=
`\pm 1.699`

Now,

The confidence interval will be:

=
`\bar x \pm (t* s)/(√(n) )`

By putting the values, we get

=
`18.6 \pm (1.699* 5.2)/(√(30) )`

=
`16.987,20.213`