The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. Choose two pregnancies independently and at random.(a) What is the expected difference in the lengths of the two pregnancies?
Q. The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. Choose two pregnancies independently and at random.(a) What is the expected difference in the lengths of the two pregnancies?
Expected Difference Calculation: The expected difference in the lengths of two independent random variables is the same as the expected value of the difference of those two variables. Since we are dealing with the same distribution for both pregnancies, the expected value of the difference is 0 because the mean of the differences between two identical distributions is 0.
Mean of Identical Distributions: To elaborate, if X and Y are two independent random variables with the same distribution, then E(X−Y)=E(X)−E(Y). Since X and Y have the same mean, E(X)=E(Y), and therefore E(X−Y)=E(X)−E(X)=0.
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