Looks familiar. It's out of Moore and McCabe problem 8.7 page 597
with a small variation.
On Mon, 9 Apr 2001, edstat-digest wrote:
> Date: Sun, 08 Apr 2001 16:12:45 GMT
> From: Jan Sjogren <[EMAIL PROTECTED]>
> Subject: Homework problem
>
> Your mail order company advertises that it ships 90% of its orders
> within three working days. You select an SRS of 100 of the 5000 orders
> received in the past week for an audit. The audit reveals that 86 of
> these orders received in the past week for an audit. The audit reveals
> that 86 of these orders were shipped on time.
>
> a) What is the sample proportion of orders shipped on time?
>
> b) If the company really ships 90% of its orders on time, what is the
> probability that the proportion in an SRS of 100 orders is as small as
> the proportion in your sample or smaller?
>
> c) A critic says, "Aha! You claim 90%, but in your sample the on-time
> percentage is lower than that. So the 90% claim is wrong." Explain in
> simple language why your probability calculation in (b) shows that the
> result of the sample does not refuge the 90% claim.
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