Question 863316
before knowing about the .13 probability
.21+.14=.35 
1-.35=.65 

65% chance the BBQ  will happen 
The .13 is for both things happening at the same time.
I am not sure if you need to deal with that. The original "or" might deal with it.
If not, it is 1-.13-.14-.21=.52=52%

so it is either .65 or .52
 that the bbq will happen.