How do you Add Percentages?
 

This is probably very simple, but math just isn't my thing.

I'm on the bubble (4 left) of a 10 man sit and go, top 3 pays.
I am in the small blinds and it is folded to me.
What I am holding doesn't matter in this case.

If i push all in, the chances that the big blind calls is 40%.
If he calls my all in, the chances that I win are 50%.

I selected both numbers at random, by the by. But they aren't important anyways.
What are my overall chances of winning this pot (either preflop or postflop)?

Re: How do you Add Percentages?
 

P(BB fold) + P(BB call) * P(winning anyway) =
0.6 + 0.4 * 0.5 = 0.8 = 80%

Re: How do you Add Percentages?
 

Thank you kind sir.