Probability Calculator
Find an event’s probability and its complement from counts of equally likely outcomes.
Formula
P(A) = favorable/(favorable + unfavorable); P(not A) = 1 − P(A)
Probability P(A) ≈ (1)÷((1)+(5)) · Complement P(not A) ≈ (5)÷((1)+(5)) · Probability as percent ≈ 100×(0.1666666667)
How to use
- Count favorable outcomes.
- Count the other, unfavorable outcomes.
- Read the probability and its complement.
Examples
- One favorable face and five others: P = 1/6 ≈ 0.16666667.
Frequently asked questions
What must the counts represent?
Distinct equally likely outcomes. The two groups must not overlap and must cover all possibilities.
Can both counts be zero?
No. There must be at least one possible outcome.
Does this work for a biased die?
No. Unequal chances need probabilities or weights for individual outcomes.
Sources
Updated: