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The length of time for an individual to wait at a lunch counter is a random...

The length of time for an individual to wait at a lunch counter is a random variable whose density function is

f(x) = (1/4)e^(-x/4) for x > 0 and = 0 otherwise

a) Find the mean and the variance

b) Find the probability that the random variable is within three standard deviations of the mean and compare Chebyshev's Theorem.

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