7) The length of a human pregnancy is normally distributed with a mean of 272 days with a standard deviation of 9 days. a) What is the probability of a pregnancy lasting more than 280 days? (1) b) What is the probability of a pregnancy lasting between 260 and 274 days?
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For part a (280 days): \[ z_a = \frac{280 - 272}{9} = \frac{8}{9} \approx 0.89 \] For part b (260 and 274 days): \[ z_{260} = \frac{260 - 272}{9} = \frac{-12}{9} = -1.33 \] \[ z_{274} = \frac{274 - 272}{9} = \frac{2}{9} \approx 0.22 \] Show more…
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