Question

For a population automobile drives in a medium-sized city (population about 100,000),
the traffic police ticketed numerous drivers speeding in school zones during school hours. The drivers’ ticketed speeds formed a normal distribution with a mean of µ = 35 (miles per hour) and ơ = 5. With these parameters, answer the associated question(s).

What is the speed someone was driving where 40 percent of the ticketed drivers were driving at or below this speed? Round to the nearest tenths place if a fraction.

Group of answer choices

30

33.75

36.3

37.8

47.5

the correct speed is a value not listed in alternatives "a" through "e"

Answer 1

µ=   35                  
σ =    5                  
P(X≤x) =   0.4000                  
                      
Z value at    0.4   =   -0.25 (excel formula =NORMSINV(   0.4   ) )
z=(x-µ)/σ                      
so, X=zσ+µ=   -0.25 *   5   +   35  
X   =   33.75 (answer)