Hypothesis Testing

[bugsy]

Hi:)
I have taken statistics on as an extra module at uni and some of the classes clash with my compulsory modules. Because of this I am missing out on quite a bit and am finding it really hard to understand.
I've been trying to do the past exam papers to help me but I can never do the hypothesis testing questions
Can anyone help me/talk me through this question?

A survey of 90 accountancy firms in London showed that only 12 were using any form of advertising. There are indications that nationally 16% of all accountancy firms advertise. Test the hypothesis that the percentage of firms in London who advertise is significantly less than the national percentage. Test at significance level = 0.05


Thanks in advance:)

[omega]

You can use a left-tailed t-test.

sample proportion is 12/90 = 0.1333
t-test statistic is (0.1333-0.16)/sqrt[0.16*(1-0.16)/90]
The critical value can be obtained from the standard normal distribution.

Hope this helps.