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The duration of human pregnancies from conception to birth varies according to a distribution approximately Normal with mean 266266 days and standard deviation 1616 days. Choose two pregnancies independently and at random.\newlineWhat is the expected difference in the lengths of the two pregnancies?\newlineWhat is the standard deviation of the difference in the lengths of the two pregnancies?

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Q. The duration of human pregnancies from conception to birth varies according to a distribution approximately Normal with mean 266266 days and standard deviation 1616 days. Choose two pregnancies independently and at random.\newlineWhat is the expected difference in the lengths of the two pregnancies?\newlineWhat is the standard deviation of the difference in the lengths of the two pregnancies?
  1. Calculate Expected Difference: Calculate the expected difference in the lengths of the two pregnancies.\newlineSince we are dealing with a normal distribution with a mean of 266266 days, the expected value (mean) of the difference between any two pregnancies chosen at random would be 00. This is because the expected value of the difference between two identical distributions is 00.\newlineCalculation: 266266=0266 - 266 = 0
  2. Calculate Standard Deviation: Calculate the standard deviation of the difference in the lengths of the two pregnancies.\newlineThe standard deviation of the difference between two independent variables is the square root of the sum of the variances of these variables. Since both pregnancies are independent and have the same standard deviation, the variance for each is the square of the standard deviation 1616 days).\newlineCalculation: Variance for each pregnancy = 162=25616^2 = 256\newlineSum of variances = 256+256=512256 + 256 = 512\newlineStandard deviation of the difference = 512=2×256=2×16\sqrt{512} = \sqrt{2 \times 256} = \sqrt{2} \times 16
  3. Finalize Standard Deviation: Finalize the standard deviation of the difference.\newlineCalculation: Standard deviation of the difference = 2\sqrt{2} * 1616 1.414\approx 1.414 * 1616 22.624\approx 22.624 days

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