posted by Jessica on .
I have a test on this tomorrow and I swear he didn't teach this and the book's not helping either, so maybe u can:
A hwy engineer knows that his crew can lay 5 miles of hwy on a clear day, 2 miles on a rainy day, and only 1 mile on a snowy day. Suppose that the probabilities are as follows:
Outcome prob/random variable: clear .6/5, rain .3/2, snow .1/1
Find the mean (expected value) and the variance
Can anyone at least tell me where to start????
X P(X) x*P(X) x^2*P(X)
5 0.6 3 15
2 0.3 0.6 1.2
1 0.1 0.1 0.1
Mean = sum x*P(X)=3.7
sum (x^2 * P(X)) = 16.3
Variance = (x^2 * P(X)) - Mean^2
=16.3 - (3.7)^2 = 2.61
Mean = 3.7 miles and variance = 2.61 miles square