A cell phone provider has 85% of its customers rank their service as "satisfactory.” Nico takes a random sample of 75 customers from this cell phone provider. What is the probability that 83% or more of this sample ranks the provider’s service as "satisfactory”?Find the z-table here.

For the sample proportion, the mean is 0.85 and the standard deviation is √(0.85 × 0.15 / 75) ≈ 0.0412. The z-score for 0.83 is (0.83 − 0.85) / 0.0412 ≈ −0.49. The probability of a sample proportion at least 0.83 is the area to the right of −0.49, about 0.686, so the answer is D, 0.686.

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