A popular restaurant chain advertises that it delivers orders within 30 minutes. Suppose the average delivery time for one restaurant is 27 minutes with a standard deviation of three minutes. One particular order delivery took 35 minutes. What is the z-score for this delivery time?

Use the z-score formula: z = (observed time − average time) ÷ standard deviation. For this delivery, z = (35 − 27) ÷ 3 = 8 ÷ 3 ≈ 2.67. So the delivery time is about 2.67 standard deviations above the average, which is choice D, 2.67.

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