STAT 110

Newton-Pepys Probability Lab

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Exact Binomial
66.51%
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Bet A (Newton / Pepys)
Roll at least 1 six with 6 dice.
Exact: 66.51% Sim: --
RATIO 6:1
Bet B
Roll at least 2 sixes with 12 dice.
Exact: 61.87% Sim: --
RATIO 6:1
Bet C
Roll at least 3 sixes with 18 dice.
Exact: 59.73% Sim: --
The Newton-Pepys Intuitive Fallacy: In 1693, Samuel Pepys asked Isaac Newton which wager to take. Intuition tempts us to think 1/6 = 2/12 = 3/18 = equal odds. But expected value linearity doesn't apply directly to event probability thresholds!

Step 1: Complementary Event Strategy

Directly computing "at least k sixes" requires summing binomial probabilities. It is vastly easier to compute the complement: the probability of fewer than k sixes and subtract from 1.

P(At least k) = 1 - P(X < k)

Step 2: Bet A Breakdown (n=6, k=1)

The only complement is getting ZERO sixes in 6 rolls. Each die has a 5/6 chance of not showing a 6.

P(Zero 6s) = (5/6)⁶ = 0.3349
P(Bet A) = 1 - 0.3349 = 0.6651 (66.51%)

Step 3: Bet B Breakdown (n=12, k=2)

Complements are getting ZERO sixes OR EXACTLY ONE six in 12 rolls.

P(X=0) = (5/6)¹² ≈ 0.1122
P(X=1) = 12 × (1/6)¹ × (5/6)¹¹ ≈ 0.2692
P(Bet B) = 1 - (0.1122 + 0.2692) = 0.6187 (61.87%)

Step 4: Story Proof - Why odds decay as n increases

As n grows, the binomial variance relative to the mean decreases, narrowing the distribution around the mean μ = n/6. For Bet C (n=18, k=3), the distribution gets tighter around 3, putting more weight on exact values < 3 than Bet A puts on 0!

Active Wager: Bet A (6 dice / ≥1 six) Harvard Stat 110 Lab
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