SOLUTION: contractor plans to use four tractors to work on a project in a remote area. The probability of a tractor functioning for a year without a break-down is known to be 80 %. If X de

Question 1150438: contractor plans to use four tractors to work on a project in a remote area. The
probability of a tractor functioning for a year without a break-down is known to be
80 %. If X denotes the number of tractors operating at the end of a year, determine the
probability mass and distribution functions of X.
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
The mean is xp=0.8*x
the variance is xp(1-p)=0.8*0.2*x=0.16x, and the sd is 0.4*sqrt(x)
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