# STAT 1430 Lecture 15: Random Variables February 26, 2019

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## Document Summary

Rule #3 for variances sums **(x an y are not independent)*: if x and y are not independent, they have a correlation, ! ( rho , then variance of x+y is: If x and y are independent what"s ! = correlation of all possible (x,y) points in population. = correlation of all (x,y) pairs in sample. Tuesday, february 26, 2019: x=price of gallon of milk, y=price of captain crunch cereal (28 oz) Mean of x = . 65; sd=sh. 50 ! Mean of y = . 89; sd=sh. 75 ! Price x and y are correlated with ! 0. 52 + 0. 752 + 2 * ( 0. 7) * 0. 5 * 0. 75 = 0. 2875no unit. Y + 2 x y: standard deviation: Rule #3 for variances - differences **(x and y are not independent)*: if x and y are not independent they have some correlation , then variance of x-y is: If x and y are independent this formula becomes:

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