A quality control engineer found that the inner and outer diameters of their ball bearin denoted respectively as X and Y, are random variables with E(X|Y = y) = 0.7 – 0.3y inch and Var(X|Y = y) = 0.0004y for all values of y. From his past experience he also knew th the mean and variance of the outer diameters were E(Y) = 0.7 inches, and Var (Y) = 0.00 squared inches. • (i) What are the conditional random variables, E(X|Y) and Var(X|Y)? • (ii) Find the mean of the inner diameters, E(X). (iii) Find the variance of the inner diameters, Var(X).
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
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