Find a 95% confidence interval for the percentage of cars on a certain highway that have poorly adjusted brakes, using a random sample of 500 cars stopped at a roadblock on that highway, 87 of which had poorly adjusted brakes.
I think I need to find k, with
n = 500, .
Not sure how to find c or s.
This is the answer, but I don't know how c or was calculated.
For c, I tried and looking up the value for .975 on the t distribution chart with 50 - 1 = 49 degrees of freedom. But 49 was not on the chart.
For , I'm not understanding why it is .