The lengths of human pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days. What is the probability that a pregnancy last at least 300 days?
A) 0.0166
B) 0.4834
C) 0.0179
D) 0.9834

Question

Quizplus · Accepted Answer

To find the probability that a pregnancy lasts at least 300 days, we calculate the Z-score for 300 days using the formula Z = (X - μ) / σ, where X is 300 days, μ is the mean (268 days), and σ is the standard deviation (15 days). This gives us Z = (300 - 268) / 15 = 32 / 15 ≈ 2.13. Looking up the Z-score of 2.13 in a standard normal distribution table or using a calculator, we find that the area to the left of Z = 2.13 is approximately 0.9834, meaning the area to the right (the probability of a pregnancy lasting at least 300 days) is 1 - 0.9834 = 0.0166.

The Lengths of Human Pregnancies Are Normally Distributed with a Mean