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Let X be a binomial random variable with n = 8 and p = 1/2. What is the value of P(|X - 4| ≤ 2)?
- 119/128
- 119/228
- 19/128
- 18/128
Correct answer: 119/128
Solution
P(|X-4|<=2)=P(2<=X<=6)=1-[P(0)+P(1)+P(7)+P(8)] = 1-(1+8+8+1)/256 = 1-18/256 = 238/256 = 119/128.
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