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A school psychologist is trying to determine the lower boundary of a confidence interval for a IQ measure that has a mean of 100 and a standard deviation of 30 and a sample size of 100. What is the lower boundary if she was to create a 95% confidence interval?

  • statistics -

    CI95 = mean + or - 1.96(sd/√n)
    ...where + or - 1.96 represents the 95% confidence interval using a z-table, sd = standard deviation, √ = square root, and n = sample size.

    With your data:
    CI95 = 100 + or - 1.96(30/√100)

    I'll let you take it from here.

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