Question

Exercise 11.4.3: Detecting a biased coin. About A gambler has a coin which is either fair (equal probability heads or tails) or is biased with a probability of heads equal to 0.3. Without knowing which coin he is using, you ask him to flip the coin 10 times. If the number of heads is at least 4, you conclude that the coin is fair. If the number of heads is less than 4, you conclude that the coin is biased. (a) What is the probability you reach an incorrect conclusion if the coin is fair

Answer 1

0.17189

0.3504

Explanation:

For a fair coin ; p = 0.5

1 - p = 0.5

P(x < 4) = p(x = 0) + p(x =1) + p(x = 2) + p(x = 3)

Recall:

P(x =x) = nCx * p^x * (1 - p)^(n - x)

Using a calculator to save time:

P(x <4) = 0.00098 + 0.00977 + 0.04395 + 0.11719

P(x < 4) = 0.17189

For a unfair coin :

p = 0.3 ; 1 - p = 1 - 0. 3 = 0.7

P(x ≥ 4) = p(x=4)+p(x =5)+p(x=6)+p(x=7)+p(x=8)+p(x=9) +P(x=10)

Recall:

P(x =x) = nCx * p^x * (1 - p)^(n - x)

Using a calculator to save time:

P(x ≥4) = 0.3504