i Forty percent of the customers of a fast food chain order

i) Forty percent of the customers of a fast food chain order the Whoppper, french 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? (2)

Solution

given p = 0.4 q = 0.6 n = 15 and r = 10 or more

the probability that 10 or more will show that the above three food items were ordered is

P ( r >= 10) = 15C10 X 0.4¹⁰X0.6⁵ + 15C11 X 0.4¹¹X0.6⁴ + 15C12 X 0.4¹² X 0.6³ + 15C13 X 0.4¹³ X 0.6² + 15C14X0.4¹⁴X0.6¹ + 15C15 X 0.4¹⁵  is the solution for the given problem.