Prob. assignment P(a) = 0.1, P(d) = 0.3, then P({a, d}) = ??

[Navyguy]

In a probability assignment P(a) = 0.1, P(b) = 0.2, P(c) = 0.4, P(d) = 0.3, then P({a, d}) = ____.

0.1 + 0.3 = 0.4, so 0.4 is my answer. Is this right? Thanks so much for checking.

 

[tkhunny]

That would be my guess, if I can decode the notation, anyway.

Why do you doubt?