How Many Trials Are Enough?

Interactive Probability & Law of Large Numbers Activity for Grades 7-10

Mathematical Foundations Simulation & Experimentation Grades 7-10

Discovering the Law of Large Numbers

In this interactive lesson, you'll explore how probability works in the real world through hands-on simulations. Learn why scientists, game designers, and statisticians run many trials to get accurate results!

Real-World Context: Gaming, Science

Math Concepts: Probability, Law of Large Numbers

H NUMBER OF TRIALS OUTCOME PROBABILITY
Introduction
Coin Flip
Dice Roll
Spinner
Challenge
Reflection

The Power of Multiple Trials

Have you ever wondered why scientists repeat their experiments many times? Or why game designers test their games over and over? The answer lies in probability and something called the Law of Large NumbersA principle that states that as a process is repeated more times, the actual outcomes will converge on the expected theoretical probability..

Think About: If you flip a fair coin 10 times, would you always get exactly 5 heads and 5 tails? Why or why not?

Key Concepts

Probability: The likelihood that a specific outcome will occur. It ranges from 0 (impossible) to 1 (certain).

Law of Large Numbers: As you increase the number of trials (like coin flips or dice rolls), the actual results will get closer and closer to the expected probability.

The chart above shows what typically happens when you flip a fair coin many times. Notice how with just a few flips, the percentage of heads can vary widely. But as you do more and more flips, the percentage gets closer to the expected 50%.

Why this matters: In the real world, understanding probability and the Law of Large Numbers helps us:

  • Design fair games
  • Conduct reliable scientific experiments
  • Make better predictions about uncertain events
  • Understand when we have enough data to draw conclusions

Coin Flip Experiment

Let's start with a simple experiment: flipping a fair coin. Theoretically, a fair coin has a 50% chance of landing on heads and a 50% chance of landing on tails.

H
T

Total flips: 0

Heads: 0 (0%)

0%

Tails: 0 (0%)

0%

Questions to Consider:

  1. After 10 flips, how close was your heads percentage to 50%?
  2. After 100 flips, did the percentage get closer to 50%?
  3. If you did 1,000 flips, what would you expect to happen?

The Law of Large Numbers in Action

With just a few flips, the results can vary widely from the expected 50% probability. This is normal! Random events don't always follow the expected pattern in small samples.

But as you increase the number of flips, something interesting happens: the actual percentage gets closer and closer to the theoretical 50%. This is the Law of Large Numbers in action.

Dice Roll Experiment

Now let's try something a bit more complex: rolling a six-sided die. Each face has a 1/6 (about 16.7%) probability of showing up on any single roll.

1

Total rolls: 0

Face Count Percentage Expected
1 0 0% 16.7%
2 0 0% 16.7%
3 0 0% 16.7%
4 0 0% 16.7%
5 0 0% 16.7%
6 0 0% 16.7%

Questions to Consider:

  1. After just 10 rolls, were all six numbers represented equally?
  2. After 100 rolls, how close were your percentages to the expected 16.7%?
  3. What's the minimum number of rolls you think would be needed to get all faces within 1% of their expected value?

When "Random" Doesn't Look Random

With a die, you have six possible outcomes instead of just two, so it can take even more rolls to see the expected distribution. This is why games that use dice often require multiple rolls or multiple dice - to smooth out the randomness.

This is also why scientists don't rely on just a few trials for their experiments. They need many data points to be confident that what they're observing isn't just due to random chance.

Spinner Experiment

Now let's try a weighted probability experiment. This spinner has four sections, but they're not equal in size. The larger sections have a higher probability of being selected.

Total spins: 0

Section Size Expected % Count Actual %
Blue (Large) 50% 50% 0 0%
Light Blue 25% 25% 0 0%
Dark Blue 12.5% 12.5% 0 0%
White 12.5% 12.5% 0 0%

Questions to Consider:

  1. After 10 spins, did the section percentages match their expected probabilities?
  2. Which sections needed more spins to get close to their expected percentages?
  3. Why might the smaller sections (Dark Blue and White) take longer to reach their expected percentages?

Uneven Probabilities and Sample Size

This experiment shows something important: outcomes with smaller probabilities often need more trials to reach their expected percentages. This is why rare events or small effects in science require larger sample sizes to detect accurately.

Think about testing a new medicine that helps 5% of patients. If you only test it on 10 people, you might not see any effect at all! But if you test it on 1,000 people, you're likely to see close to 50 people helped, which gives you much more confidence in the results.

The Sample Size Challenge

Now it's your turn to design an experiment! Your goal is to find out how many trials are needed to get reliable results for different probability scenarios.

Design Your Experiment

Choose a probability experiment and decide how many trials to run. Then predict what you think will happen!

10 1000

Make your prediction:

How close to the theoretical probability do you think your results will be?

Results

Your experiment results will appear here after you run the experiment.

Understanding Sample Size

Different scenarios require different numbers of trials to get reliable results:

Scenario Approximate Trials Needed for Reliable Results
50/50 probability (coin flip) 100+ trials to get within 5% of expected
1 in 6 probability (dice roll) 300+ trials to get within 5% of expected
Rare events (5% probability) 500+ trials to detect reliably
Very rare events (1% probability) 1000+ trials to detect reliably

Think About: Why do rarer events require more trials? How might this apply to situations like testing a rare side effect of a medication?

Reflection: Real-World Applications

Now that you've experimented with probability and the Law of Large Numbers, let's think about how these concepts apply in the real world.

Key Takeaways:

  1. Small samples can be misleading - A few trials often don't reflect the true probability.
  2. The Law of Large Numbers - As you increase the number of trials, results tend to get closer to the expected probability.
  3. Sample size matters - Rarer events require more trials to detect accurately.
  4. Statistics help us understand randomness - Randomness doesn't mean each outcome happens equally often in small samples.

Discussion Prompts:

  1. How does understanding probability and the Law of Large Numbers apply to gaming and science?
  2. Why is simulation and experimentation important in the real world?
  3. How might these mathematical skills be useful in future careers?

Real-World Applications

Gaming

Game designers need to understand probability to:

  • Create balanced gameplay
  • Set appropriate difficulty levels
  • Make games fair but still exciting
  • Design random loot systems that feel rewarding

For example, if a game has a 1% chance to drop a rare item, players might need to defeat hundreds of enemies before finding one. Understanding this helps designers determine if that rate feels fair and fun.

Science

Scientists rely on probability and large samples to:

  • Test whether treatments work better than placebos
  • Determine if results are statistically significant
  • Calculate margins of error in surveys and polls
  • Identify rare side effects of medications

Clinical trials often need thousands of participants to reliably detect both beneficial effects and rare side effects of new treatments.

Your Reflection

Write a short reflection on what you've learned about probability and the Law of Large Numbers. Consider these questions:

  • What surprised you about the experiments?
  • How has this changed how you think about probability in everyday life?
  • Can you think of a situation where you've seen the Law of Large Numbers in action?

Further Exploration

Want to learn more? Try these activities:

  • Create your own probability experiment and collect data
  • Analyze the odds in a favorite board or card game
  • Research how statistics are used in sports analytics
  • Explore how polling organizations determine sample sizes

Career Connections

Understanding probability and the Law of Large Numbers is essential for careers in:

  • Game Design and Development
  • Scientific Research
  • Data Science and Analytics
  • Medical Research and Testing
  • Finance and Risk Assessment
  • Quality Control in Manufacturing
  • Market Research and Polling

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