Probability low enough? (over-booking seats on flight)

[statshelp]

1 more that I need help with!!

Question:
An airline has a policy of booking 21 persons on an airplane that can only seat 20. Past studies show that 88% of the booked passengers actually arrive for the flight. Find the probability that if the airline books 21 persons, not enough seats will be available. Is this probability low enough so that overbooking is not a real concern for passengers?

My work:
n=21
p=.88
q=.12
21C21 (.88)^21(.12)^0
= .0683
= 7%
No, because that means that there is a 7% chance of not having enough seats. Too high, I wouldn't want to take that risk.

I feel like I am missing steps, but do not know where? Please help!

 

[r_yackel]

Re: Probability low enough?

My work:
n=21
p=.88
q=.12
21C21 (.88)^21(.12)^0

just out of curiosty shouldnt it be 21C20??

 

[royhaas]

Why do you think you are missing steps? Your setup appears correct. Try writing in words what your calculation means.

 

[statshelp]

Thanks for the feedback. I went through it step by step and have a better understanding now.