Originally Posted by

**Brennan010** Adding A and B for atleast 1 doesn't work, because they are both separate probabilities, unlike dice or a coin.

If you were looking for at least a 1, 2, or 3 on a dice, you would add all 3 probabilities together, so 1/6 + 1/6 + 1/6 = 1/2

However, this is more like the chance of it raining out, if you have a 75% chance that it will rain on days A and B, there's a (25%*25%) 12.5% chance that it won't rain either day, therefore a (1-.125) 87.5% chance that it will rain at least one day.