Mathematics for IGCSE & O level - Probability (Section 6 - No. 3)

A weather forecast states a 20% chance of rain. What are the odds against rain (in fractional form)?

1/5

4/5

1/4

4/1

If the chance of rain is 20%, the chance of no rain is 80%. This gives odds of 80:20 or 4:1 (against rain). Expressed as a fraction, this is 4/1.