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4.2 Estimating Probabilities Using Simulation

Part of Probability, Random Variables, and Probability Distributions in AP® Statistics. Read the opening section, then create a free account for the full interactive lesson, practice, and progress tracking.

Designing and Running a Simulation

A simulation uses chance to model a random situation. Here is the systematic process:

Step 1: State the question — What probability do we want to estimate? Step 2: Assign random digits — Map digits 0-9 to outcomes Step 3: Simulate one trial — Use random digits to represent one occurrence Step 4: Repeat many trials — 50-100+ is typical Step 5: Compute the estimate — Count favorable trials / total trials

Example: Three free throws, each made 70% of the time. Estimate P(make all 3){P(\text{make all 3})}:

  • Assign: 0-6 = made shot, 7-9 = missed shot
  • One trial = 3 consecutive random digits
  • Count trials where all 3 digits are 0-6
  • After 50 trials: if 25 meet the condition, P^≈25/50=0.50{\hat{P} \approx 25/50 = 0.50}

True probability: 0.73=0.343{0.7^3 = 0.343} — simulation should approach this with more trials.

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