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Math Help - Specification Hours

  1. #1
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    Specification Hours

    Random sample of 120 customersís spent an average of 9.2 hours on their professional job with a sample standard deviation of 5.1 hours. Calculate the specification hours with confidence of 95%.
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  2. #2
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    Quote Originally Posted by magentarita View Post
    Random sample of 120 customersís spent an average of 9.2 hours on their professional job with a sample standard deviation of 5.1 hours. Calculate the specification hours with confidence of 95%.
    I have not heard of specification hours. It looks like you are supposed to calculate the confidence interval with 95% confidence level.

    The Central Limit Theorem (which the general rule of thumb says is ok to invoke for N\geq 30) tells us that \frac{\bar{X}-\mu}{S \sqrt{N}} is approximately normally distributed with mean 0 and std dev 1.

    So then the confidence interval is given by \bar{X}\pm z_{\alpha/2}S/\sqrt{N} where z_{\alpha/2} is defined by \mathrm{P}(-z_{\alpha/2}\leq Z \leq z_{\alpha/2})=1-\alpha (Z is from the standard normal distribution). I'm assuming that you have already seen where these formulas came from.

    So from a standard normal distribution table z_{\alpha/2}=1.96. So just plug away.
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  3. #3
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    ok...

    Quote Originally Posted by meymathis View Post
    I have not heard of specification hours. It looks like you are supposed to calculate the confidence interval with 95% confidence level.

    The Central Limit Theorem (which the general rule of thumb says is ok to invoke for N\geq 30) tells us that \frac{\bar{X}-\mu}{S \sqrt{N}} is approximately normally distributed with mean 0 and std dev 1.

    So then the confidence interval is given by \bar{X}\pm z_{\alpha/2}S/\sqrt{N} where z_{\alpha/2} is defined by \mathrm{P}(-z_{\alpha/2}\leq Z \leq z_{\alpha/2})=1-\alpha (Z is from the standard normal distribution). I'm assuming that you have already seen where these formulas came from.

    So from a standard normal distribution table z_{\alpha/2}=1.96. So just plug away.
    I thank you for your time and effort.
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