If the probability of rain tomorrow is 0.25, what are odds in favor?

• A. 3:1
• B. 1:3
• C. 1:4
• D. 4:1

Answer: (B)

Odds in favor compare how likely the event is to happen versus not happen. It’s the ratio p to 1−p. With a 0.25 chance of rain, the odds in favor are 0.25 : 0.75, which simplifies to 1 : 3. So rain is three times less likely than no rain, and the odds in favor are 1 to 3. Remember, this is different from probability (which is 0.25 for rain); odds express a relative likelihood between the event and its complement.