Probability rule for calculating the likelihood of two heads in a row when flipping a coin twice.

A probability tree diagram illustrating the outcomes of two coin flips, showing branches for heads and tails with probabilities of 0.5 each, leading to four possible outcomes: Heads-Heads, Heads-Tails, Tails-Heads, and Tails-Tails, with the calculation for the probability of two heads in a row (0.5 × 0.5 = 0.25) highlighted.