On a fair 6-sided die each number has an equal probability p of being rolled. When a fair die is rolled n times, the most likely outcome (the mean) is that each number will be rolled np times, with a standard deviation of σ=√ (np (1-p)). Brandon rolls a die 200 times. He will conclude that the die is loaded (unfair) if the number of time any number is rolled is outside of the 1.5 standard deviations of the mean. What are the minimum and maximum number of times a number can be rolled without Brandon concluding that the die is loaded?

Question

Mathematics

Juliet Bartlett

25 September, 16:15

On a fair 6-sided die each number has an equal probability p of being rolled. When a fair die is rolled n times, the most likely outcome (the mean) is that each number will be rolled np times, with a standard deviation of σ=√ (np (1-p)). Brandon rolls a die 200 times. He will conclude that the die is loaded (unfair) if the number of time any number is rolled is outside of the 1.5 standard deviations of the mean. What are the minimum and maximum number of times a number can be rolled without Brandon concluding that the die is loaded?

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Answers (1)

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Braelyn Bell · Answer 1

A 1.5 standard deviation above the mean is

np + 1.5 √ (np (1-p))

We are given with

np = 200

p = 200/n

The standard deviation is

√200 (1-200/n))

Substituting

200 + 1.5 √200 (1-200/n))

By inspection, if the value of n is 200, then the radical will result to the value of 1. Only by increasing the value of n greater than 200 will the radical result to a value of less than 1 and decreasing the spread of the mean.

The answer is

the minimum is 201

the maximum is infinity