According to a flight statistics website, in 2009, a certain airline had the highest percentage of on-time flights in the airlines industry, which was 80.8%. assume this percentage still holds true for that airline. use the normal approximation to the binomial distribution to complete parts a through c below. a. determine the probability that, of the next 30 flights from this airline, less than 20 flights will arrive on time. p(xless than20)equals 0.0140 (round to four decimal places as needed.) b. determine the probability that, of the next 30 flights from this airline, exactly 24 flights will arrive on time. p(xequals24)equals 0.1822 (round to four decimal places as needed.) c. determine the probability that, of the next 30 flights from this airline, 25, 26, 27, or 28 flights will arrive on time. p(25less than or equalsxless than or equals28)equals 0.4279 (round to four decimal places as needed.)

a) 0.0139; b) 0.1809; c) 0.4278

Step-by-step explanation:

We use a normal approximation to a binomial distribution for these problems.

The sample size, n, for each is 30; p, the probability of success, is 0.808.  This makes the mean, μ = np = 30(0.808) = 24.24.  The standard deviation,

σ = √(npq) = √(30(0.808)(1-0.808)) = √(30(0.808)(0.192)) = √4.65408 = 2.1573

For part a,

We are asked for P(X < 20).  Using continuity correction to account for the discrete variable, we find

P(X < 19.5)

z = (19.5-24.24)/(2.1573) = -4.74/2.1573 = -2.20

Using a z table, we see that the area under the curve to the left of this is 0.0139.

For part b,

We are asked for P(X = 24).  Using continuity correction, we find

P(23.5 < X < 24.5)

z = (23.5-24.24)/2.1573 = -0.74/2.1573 = -0.34

z = (24.5-24.24)/2.1573 = 0.26/2.1573 = 0.12

Using a z table, we see that the area under the curve to the left of z = -0.34 is 0.3669.  The area under the curve to the left of z = 0.12 is 0.5478.  The area between them is then

0.5478-0.3669 = 0.1809.

For part c,

We are asked to find P(25 ≤ X ≤ 28).  Using continuity correction, we find

P(24.5 < X < 28.5)

z = (24.5-24.24)/2.1573 = 0.26/2.1573 = 0.12

z = (28.5-24.24)/2.1573 = 4.26/2.1573 = 1.97

Using a z table, we see that the area under the curve to the left of z = 0.12 is 0.5478.  The area under the curve to the left of z = 1.97 is 0.9756.  The area between them is 0.9756 - 0.5478 = 0.4278.