I know don't know if this right P(X)<115)= 12.1 (115-mean) how do I get the mean or is there a formula that can help me solve this?

A population of line voltages has a standard deviation of 1.20 volts. What value would the mean line voltage have to be so that 12.1% of the line voltages fell below 115V?

asked by Will
  1. Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.121) and its Z score. Z score = -1.27 is standard deviations below the mean.

    115 + 1.27(1.2) = mean

    posted by PsyDAG

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