Question

The mean cost of domestic airfares in the United States rose to an all-time high of $385 per ticket. Airfares were based on the total ticket value, which consisted of the price charged by the airlines plus any additional taxes and fees. Assume domestic airfares are normally distributed with a standard deviation of $120. Use Table 1 in Appendix B.

a. What is the probability that a domestic airfare is $550 or more (to 4 decimals)?

b. What is the probability that a domestic airfare is $250 or less (to 4 decimals)?

c. What if the probability that a domestic airfare is between $300 and $480 (to 4 decimals)?

(I tried putting it in Excel, answer is not .0668 for part A, .1093 for part B, and .6325 for part C) May I know the answers to these please?

Answer 1

Solution :

Using Excel,

a)

P(X $\geq$ 550)

= 1 - NORM.DIST(550,385,120,TRUE)

= 0.0846

Probability = 0.0846

b)

P(X $\leq$ 250)

= NORM.DIST(250,385,120,TRUE)

= 0.1303

Probability = 0.1303

c)

P(300 < x < 480)

= NORM.DIST(480,385,120,TRUE) - NORM.DIST(300,385,120,TRUE)

= 0.5464

Probability = 0.5464