Bernoulli Trials & Binary Coin Flip Probability
A fair coin toss represents the foundational model of a Bernoulli trial — a random experiment with exactly two mutually exclusive outcomes: Heads ($X=1$) and Tails ($X=0$), each with probability $p = 0.5$.
1. Single Flip Bernoulli Probability
P(Heads)=p = 0.50 (50%),P(Tails)=1 − p = 0.50 (50%)
2. Binomial Distribution Formula (k Heads in n Flips)
P(K = k)=×pᵏ × (1 − p)ⁿ⁻ᵏ
n!k! × (n − k)!
Step-by-Step Probability Breakdown (Probability of Exactly 3 Heads in 5 Flips)
Step 1: Calculate Combinations C(5, 3)
C(5, 3) = 5! / (3! × 2!) = (120) / (6 × 2) = 10 distinct combinations
Step 2: Calculate Probability per Path
(0.5)³ × (0.5)² = (0.5)⁵ = 0.03125 (1/32)
Step 3: Total Binomial Probability
P(3 Heads in 5 Flips)=10 × 0.03125=0.3125 (31.25%)
Coin Streak Probability Reference
| Streak Length (Consecutive) | Formula (0.5ⁿ) | Decimal Probability | Odds (1 in X) |
|---|---|---|---|
| 2 Consecutive Heads | (0.5)² | 25.0% | 1 in 4 |
| 5 Consecutive Heads | (0.5)⁵ | 3.125% | 1 in 32 |
| 10 Consecutive Heads | (0.5)¹⁰ | 0.0977% | 1 in 1,024 |