### CFA Practice Question

There are 434 practice questions for this study session.

### CFA Practice Question

Sixty percent of the customers of a fast food chain order the Whopper, fries, and a drink. If a random sample of 15 cash register receipts is selected, what is the probability that 10 or more will show that the above three food items were ordered?
A. 0.403
B. 0.186
Explanation: This is a binomial probability. The probability of getting r successes out of n trials, where the probability of success of each trial is p and probability of failure of each trial is q (where q = 1 - p), is given by: n!(pr)[q(n-r)]/r!(n-r)!. Therefore, we need to find the probability of getting 10, 11,12,13,14,15 successes and add them up. Here, n=15, p=0.6, and q=0.4. r changes from 10 to 15.

p(10 successes) = 15!(0.610)(0.45)/10!(15-10)! = 0.1859
p(11 successes) = 15!(0.611)(0.44)/11!(15-11)! = 0.1268
p(12 successes) = 0.0634
p(13 successes) = 0.0219
p(14 successes) = 0.0047
p(15 successes) = 0.00047

The sum of all the probabilities is 0.403.