aircraft probability

Hello, I had a multi step problem based on departure and arrival stats of a particular plane.
The only one I am stuck on however is as follows:
Given:
A plane flight departs (on-time) = P(d)=.83, and arrives (on-time) = P(a)=.82...and prob. that it departs & arrives on time is .78:

1. what is the prob. that an aircraft will arrive on time or depart on time?
- ???
Is this too easy?? - Is it simply .78 then from the given conditions?

\(\displaystyle \text{P(A or B)=P(A)+P(B)-P(A and B)}\)

Thanks, I came up with 0.87