# Hypothesis Testing Homework

#### billy_bob_boy2291

##### New Member
Please help, I don't know where to start with this question.

A large manufacturing company found that in the past 32% of all supply shipments were received late. A new system was recently implemented. A random sample of 118 deliveries since the system was installed revealed that 22 deliveries were late.

The company wants to use the sample to test whether the proportion of late deliveries was reduced by the new system. What is the observed value of the appropriate test statistic?

#### trinker

##### ggplot2orBust
Generally, you should try to attack the problem somewhat on your own before asking for help. It makes us want to provide assistance because we think you're attempting to learn rather than to get a grade on HW.

Now, let me reiterate what you said: you have an accepted population mean. You have no accepted standard deviation. You have a sample with a mean different than the accepted mean (simple 5th grade statistics should help you come up with the mean of the sample).

You have an independent one sample. This is your hint. Google that. As is generally the case with a statistical hypothesis test, you have to generate Ho and Ha, find a critical value using a distribution (not telling you what distribution to use yet), find the test statistic and make a decision using the critical value of rejecting or accepting Ho.

#### billy_bob_boy2291

##### New Member
Thanks for your help, but I still can't seem to get the right answer and I would really like to understand how to do these problems.

I know the formula for T is sample mean - population mean over standard deviation. So then I need to find the standard deviation which I can't seem to figure out.

My workbook gives the value of T as -3.11, using that I have tried to work backwards to find the standard deviation but it is still not making sense.

I would greatly appreciate if you could point me in the right direction.

#### Dragan

##### Super Moderator
o find the standard deviation but it is still not making sense.
Billy_bob: The standard deviation is: Sqrt [ n*p*(1-p) ] = 5.06723

where n = 118 and p = .32.

Look at your book (or notes), mkay.