ProbLab

Probability Calculator

Favorable outcomes over total outcomes — the foundation of probability.

The simplest probability rule

P(A) is just favorable outcomes divided by total possible outcomes, assuming each outcome is equally likely — everything else in probability theory builds on this single ratio.

Combining independent events

When two events don't influence each other (like two separate coin flips), the probability of both happening is simply P(A) × P(B) — this calculator shows that multiplication step explicitly.

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ProbLab

Probability Calculator

Favorable outcomes over total outcomes — the foundation of probability.

Favorable outcomes (A)

Total possible outcomes

Favorable outcomes (B, optional)

P(A): 0.077
P(not A): 0.923
P(A and B): 0.019

What you entered

Favorable: 4Total: 52

1
P(A) = favorable ÷ total outcomes
4 ÷ 52= 0.0769
2
P(not A) = 1 − P(A)
1 − 0.0769= 0.9231
3
P(B) = favorable(B) ÷ total outcomes
13 ÷ 52= 0.25
4
P(A and B), assuming independence
0.0769 × 0.25= 0.0192

Result

P(A): 0.077

With 4 favorable outcomes out of 52 total, P(A) = 0.077 — about 7.7% likely.

The simplest probability rule

P(A) is just favorable outcomes divided by total possible outcomes, assuming each outcome is equally likely — everything else in probability theory builds on this single ratio.

Combining independent events

When two events don't influence each other (like two separate coin flips), the probability of both happening is simply P(A) × P(B) — this calculator shows that multiplication step explicitly.