confidence interval

[mandarine]

I´m given that 200 students took a test. 50 failed.
I´m not given any standard deviation.

Find 95% confidence interval for the proportion/part that failed.

How do I do that without any standard dev.

[beemzet]

you can figure out the standard error using the proportion.
take a look at this http://davidmlane.com/hyperstat/B9168.html