In a certain breed of cattle, the length of gestation has a mean of 284 days and a standard deviation is 5.5 days. What is the z-score for a gestation period that lasts 290 days?

Use the z-score formula: z = (value − mean) ÷ standard deviation. For 290 days, z = (290 − 284) ÷ 5.5 = 6 ÷ 5.5 ≈ 1.09. The gestation period is above the mean, so the z-score is positive; the correct choice is 1.09.

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