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    Confidence Interval Questions

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    A confidence interval is desired for the true average stray-load loss (watts) for a certain type of induction motor when the line current is held at 10 amps for a speed of 1500 rpm.

    Assume that stray-load loss normally distributed with sigma = 2.3

    Give answer to three decimal places.
    Compute a 95% confidence interval for when n = 25 and xbar = 55.4
    What is the lower bound?

    Give answer to three decimal places
    Compute a 95% confidence interval for when n = 25 and xbar = 55.4
    What is the upper bound?

    Give answer to three decimal places.
    Compute a 95% confidence interval for when n = 100 and xbar = 55.4
    What is the lower bound?

    Give answer to three decimal places
    Compute a 95% confidence interval for when n = 100 and xbar = 55.4
    What is the upper bound?

    Give answer to three decimal places.
    Compute a 99% confidence interval for when n = 100 and xbar = 55.4
    What is the lower bound?

    Give answer to three decimal places.
    Compute a 99% confidence interval for when n = 100 and xbar = 55.4
    What is the upper bound?

    How large must n be if the width of the 99% interval is to be 1.5?

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    Solution Preview

    A confidence interval is desired for the true average stray-load loss (watts) for a certain type of induction motor when the line current is held at 10 amps for a speed of 1500 rpm. Assume that stray-load loss normally distributed with = 2.3

    To calculate the 95% confidence interval, we use the following formula:

    Here, x-bar is always going to be 55.4, n is either going to be 25 or 100, and sigma (the standard deviation) is going to be 2.3.

    Give answer to three decimal places.
    Compute a 95% confidence interval for when n = 25 and = xbar55.4
    What is the lower bound?

    Give answer to three decimal places
    Compute a 95% confidence interval for when ...

    $2.19

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