Probability Coin Flip Experiment
Flip a coin 100 times and record heads vs. tails. Discover that probability predictions get more accurate with more data — a core concept in math and science.
What You'll Need
- 1A coin
- 2Paper and pencil for tally chart
- 3Calculator (optional)
What You'll Need
A coin
Paper and pencil for a tally chart
A calculator (optional, for percentages)
How to Play
Make a tally chart: Heads column and Tails column.
Predict: "Out of 100 flips, how many heads?" Write it down.
Flip and tally in sets of 10.
After 10 flips: "6 heads, 4 tails. Not 50-50 yet."
Continue. After 50 flips, check the running total.
At 100 flips, count finals: "48 heads, 52 tails."
"Close to 50-50! More flips = closer to prediction. That's the law of large numbers."
The Math Behind It
Each coin flip has a 50% chance of heads and 50% chance of tails, but that doesn't mean every 10 flips will be 5-5. Small samples are "noisy" — they vary a lot. As you add more data, the proportion smooths out toward 50%. This is the law of large numbers, and it's the reason we need large sample sizes in science, polls, and medical studies.
Tips
Graph the running percentage of heads after every 10 flips. The line will zigzag early and stabilize near 50%.
After 100 flips, ask: "What if someone got 90 heads? Would you think the coin is fair?" This introduces statistical thinking.
Try a die: predict how often you'll roll a 6 out of 60 throws (should be about 10 times).
Compare 10 flips vs. 100 flips. Which is closer to 50-50? This demonstrates why sample size matters.
For advanced kids, calculate the percentage after each set: 6/10 = 60%, 23/50 = 46%, 48/100 = 48%.
Frequently Asked Questions
How long does this activity take?
This activity takes about 25 min, with 0 min of preparation time beforehand.
What materials do I need?
You'll need: a coin, paper and pencil for tally chart, calculator (optional).
What age is this activity for?
This activity is designed for 8-12 years. You can adapt it for younger or older children by adjusting the complexity.
Can this be done indoors?
This activity is designed for indoor play, making it perfect for rainy days or when you're staying inside.
How difficult is this activity?
This is an easy activity that requires minimal setup and supervision. Great for busy days or when you need something quick.
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