John Wheeler, WDAY, Published June 15 2012
Weather Talk: What’s the correct answer on possibilities of rain?If the chance of rain is 50 percent on Saturday and 50 percent on Sunday, then what is the probability that it will rain at all over the weekend?
If you want to discuss the problem with other readers, hold on. If you want to know the answer, then read on.
The answer is not 100 percent. Just adding up the two probabilities does not work. You have to figure out all the possibilities. With the chance either day at 50 percent, there become four possibilities overall: 1) It rains both days. 2) It rains on Saturday but not Sunday. 3) It rains on Sunday but not Saturday. 4) It does not rain either day.
So for three of the four possibilities, it does, indeed, rain over the weekend. So the probability is 75 per cent.
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