Assuming what you gave is the only data we can use and that both players are independent, then just use the product of their probabilities.
P(A and B) = P(A) x P(B)
But if there are other facts you have to reveal, then the product of their probabilities will be of no use.
Ok but still... Not enough info. I mean it's entirely possible for player A to have less than 20 points and player B to have more than 10 in a way that they sum to over 30. So we don't have enough info.
Look up "convolution". But yeah the info you gave isn't nearly enough for a discrete random variable and even less so for a continuous one. Just a suggestion for the future - give all relevant details. We have 9 posts here before we even got an outline of what you are actually trying to do. We could have saved some time if you outlined your actual problem.