Question

A certain car model has a mean gas mileage of 31 miles per gallon (mpg) with a standard deviation 3 mpg. A pizza delivery company buys 43 of these cars. What is the probability that the average mileage of the fleet is greater than 30.7 mph

Answer 1

Solution :

Given that,

mean = = 31

standard deviation = = 3

n = 43

= 31

= / n = 3 / 43 = 0.4575

P( > 30.7)

= 1 - P( < 30.7)

= 1 - P[( - ) / < (30.7 - 31) / 0.4575]

= 1 - P(z < -0.66)

Using z table,    

= 1 - 0.2546

= 0.7454

Probability = 0.7454