7 According to The Vancouver Sun December 18 2010 McDonalds

7) According to The Vancouver Sun (December 18, 2010) McDonald’s chicken fajita is labeled as having 5 grams of fat on average with a standard deviation of 1.1 grams. They did a sample of 3 fajitas, and found the average to be 8.68 grams of fat. If we assume the label is correct, and we assume fat is normally distributed, what is the probability of an average of 8.68 grams or greater?

Solution

Chicken fajita x is normal with (5, 1.1)

n = sample size = 3

x bar = 8.68

Std error = 1.1/rt 3 = 0.6351

P(X bar>8.68)

z score = 3.68/0.6351

= 5.79

P(Z>5.79) = 0.000

Hence probability of an average of 8.68 grams or greater = 0.0000