Poisson Distribution

#1
What is the probability there are at least 24 accidents at the intersection in a year if the mean number of accidents per month is 2.2? (answer=0.693)

I keep getting 0.706, which is close to the listed answer, but I'm not sure if it is correct.

My attempt:
P(X≥24) = P(X>24)+P(X=24) = 1-P(X≤24)+P(X=24)
= (using excel) = 1-POISSON(24, 26.4, 1)+POISSON(24, 26.4, 0) = 0.706

Thanks.
 

Dason

Ambassador to the humans
#2
Your answer looks fine to me. I think whoever wrote the key was wrong. I tried figuring out if it was just a rounding issue but I couldn't get their answer playing any trick with different rounding schemes.