X
= Number of people who don't turn up
~ Bin(120, 0.025)
= Poisson(3) . . . . . approximately
Using the approximation,
P(more than 116 people arrive for flight)
= P(X <= 3)
= e^(-3)(1 + 3 + 3^2/2 + 3^3/6)
= 0.647
P(there are empty seats)
= P(X >= 5)
= 1 - P(X <= 4)
= 1 - e^(-3)(1 + 3 + 3^2/2 + 3^3/6 + 3^4/24)
= 0.185