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Old June 29th, 2009, 11:11 PM
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Quote:
Originally Posted by kclark36 View Post
Given a random variable X with distribution N(mu,225) how can I find the sample size n required for a 95% confidence interval for the mean mu with an error of at most epsilon=0.01?

The only formula I can find is n=(z^2*s^2)/.25 Can I somehow use the population variance (take the square root of 225) and substitute it into an equation? I hope someone can help me. My search through websites has only made it worse. THANKYOUUUU!
Since variance is given to you, you can apply the following formula n=\frac{z_{\alpha/2}^2\sigma^2}{\varepsilon^2}, where \sigma=15 and \varepsilon=0.01. Can you find z_{0.025} and take it from here?
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