Question

In a busy coffee shop, which is a member of an international chain of coffee shops, 40% of customers order a pastry in addition to their drink. If 20 customers were selected at random during one business day, what is the probability that at least 11 of them did not order a pastry with their drink. Round your answer to 4 decimal places.

Answer 1

0.7553

Explanation:

Given that in a busy coffee shop, which is a member of an international chain of coffee shops, 40% of customers order a pastry in addition to their drink.

Hence for 20 customers selected at random during one business day, x the no of customers who did not order a pastry with their drink is binomial since each customer is independent and there are only two outcomes.

X is binomial with n =20 and p = 1-0.4 = 0.60

q = 0.4

the probability that at least 11 of them did not order a pastry with their drink

=
`P(x\geq 11) =1-0.2447\\= 0.7553`

Note that binomial prob

`P(X=x) = 20Cx (0.6)^x (0.4)^(20-x)`