Question

The cost of unleaded gasoline in the Bay Area once followed a normal distribution with a mean of $4.74 and a standard deviation of $0.16. Sixteen gas stations from the Bay area are randomly chosen. We are interested in the average cost of gasoline for the 28 gas stations. Find the exact probability that the average price for 28 gas stations is less than $4.69.

Answer 1

Solution :

Given that ,

mean = = 4.74

standard deviation = = 0.16

n = 28

=   = 4.74

= / n = 0.16 / 28 = 0.0302

P( < 4.69) = P(( - ) / < (4.69 - 4.74) / 0.0302)

= P(z < -1.65)

Using z table

= 0.0495