Determining sample size needed to test hypothesis

[Orikon]

I always do questions on school that ask for a test of hypothesis where the sample data is already give, but what if you want to do it the other way around, by first figuring out what sample size is needed to test a hypothesis at a given accuracy. Is that possible?

 

[EnumaElish]

Sure. Just solve the test statistic for n; the value of n that equates the test stat. to the critical value (given the values of all other parameters) is your answer.