Should add the probabilities or multiply them?

[Lyn05]

Hello. I'm new to this forum and I need help on this question:

Team A is playing a football match against Team B. if the probability that A will win is 4/11 and the probability that B will win is 2/11, find the probability that the match will be a draw.


I'm not sure if I should add the probabilities or multiply them, and then subtract the result from 1.


So it's either:

A) P(match will be a draw)= 1-(4/11 +2/11)
=5/11

or:

B) P(match will be a draw)= 1-(4/11)(2/11)
=113/141

Thanks a lot for any assistance provided!

Ps: Is this considered as asking for answers directly?

 

[Russell Berty]

Here is a Hint:

Let Pa be the probability that team A wins.
Let Pb be the probability that team b wins.
Let Pd be the probability of a draw.

You sample space has only three events: { A wins, B wins, Draw}

Exactly one of the three events will happen. In other words "A wins OR B wins OR Draw".

So, what can you say about Pa + Pb + Pd ?

 

[Lyn05]

Oh! So Pa + Pb + Pd = 1, therefore Pd= 1-(4/11 +2/11)
=5/11
Thank you very much!