A particularly long traffic light at an intersection is green 20% of the time. A car approaches this intersection once each day. Let X represent the number of days the car encounters a green light. Assume that each day represents an independent trial:
a)Find the probability that the light is green on exactly three days over a ten day period.
b)Find the probability that the light is green on at least three days over a ten day period.
c)Find the expected value of the number of days the car encounters a green light over a ten day period.
d) Find the standard deviation of the number of days the car encounters a green light over a ten day period.