When finding the margin of error for the mean of a normally distributed population from a sample, what is the critical probability, assuming a confidence level of 86%?

For an 86% confidence level, the middle area under the normal curve is 0.86, leaving 1 − 0.86 = 0.14 outside the interval. The upper critical value has probability 1 − 0.14/2 = 0.93 to its left, so the critical probability is 0.93 (choice C).

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