Posted by Hannah on Wednesday, May 23, 2012 at 9:32pm.
An insurance company checks police records (in a city) on 500 accidents selected at
random and notes that teenagers were at the wheel in 120 of them. It is desired to test
if this information indicate that more than 20% of auto accidents involve teenage drivers
in the city. State the decision about H0 and make the conclusion about Ha.

statistics (college  MathGuru, Thursday, May 24, 2012 at 7:14pm
You can try a proportional onesample ztest for this one since this problem is using proportions.
Using a formula for a proportional onesample ztest with your data included, we have:
z = .24  .20 >test value (120/500 is .24) minus population value (.20) divided by
√[(.20)(.80)/500] > .80 represents 1.20 and 500 is sample size.
Finish the calculation. Remember if the null is not rejected, then there is no difference. If the null is rejected, then p > .20.
I hope this will help.