In: Statistics and Probability
A radar unit is used to measure the speed of cars on a highway
during rush hour traffic. The speeds of individual cars are
normally distributed with a mean of 55 mph and a standard deviation
of 3.2 mph. Find the probability of the following events:
(a) A car traveling faster than average.
(b) A car traveling over 65 mph
(c) A car traveling between 48 and 50 mph.
Mean = = 55
Standard deviation = = 3.2
a)
We have to find the probability that a car traveling faster than average.
That is we have to find P(X > 55)
For finding this probability we have to find z score.
That is we have to find P(Z > 0)
P(Z > 0) = 1 - P(Z < 0) = 1 - 0.5 = 0.5
b)
We have to find the probability that a car traveling over 65 mph.
That is we have to find P(X > 65)
For finding this probability we have to find z score.
That is we have to find P(Z > 3.13)
P(Z > 3.13) = 1 - P(Z < 3.13) = 1 - 0.9991 = 0.0009
c)
We have to find probability that a car traveling between 48 and 50 mph.
That is we have to find P(48 < X < 50)
For finding this probability we have to find z scores.
That is we have to find P( - 2.19 < Z < - 1.56)
P( - 2.19 < Z < - 1.56) = P(Z < - 1.56) - P(Z < - 2.19) = 0.0591 - 0.0144 = 0.0447