ajit257 wrote:
why are we adding .7..how do I figure out whether it is OR/AND solution to see if it has to be added or multiplied
To figure out whether you need OR/AND, focus on how you speak about it.
You say, "I need a shirt AND a trouser" - AND so multiplication
"I need a shirt OR a T-shirt" - OR so addition
Here you say: It will Rain OR Shine
Rains - probability of party is 15%
Shines - probability of party is 70%
Since it will Rain OR Shine, total probability = 15% + 70% = 85%
Bob will have his picnic if: there is no rain (0.7) AND he goes (1) OR there is a rain (0.3) AND he still goes (0.5).