16Hit1600
Problem-Solving and Data AnalysisEasy–MediumEither of two events that cannot both happen

Problem-Solving and Data Analysis practice question

On a given day, the probability of rain is 0.3 and the probability of snow is 0.1, and it cannot both rain and snow on the same day. What is the probability that it rains or snows?

Answer: 0.4 or .4 or 2/5

For events that cannot happen together, the probability of one OR the other is the sum: 0.3 + 0.1 = 0.4.

Common wrong answers

If you answered 0.03
0.03 multiplies the probabilities, which is for BOTH happening — impossible here anyway.
If you answered 0.2
0.2 is 0.3 − 0.1; probabilities of 'or' are added.
If you answered 0.6
0.6 is 1 − 0.4, the probability of NEITHER rain nor snow.

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