Tabulation of a strike vote showed that 90% of those voting cast their ballot in favour of strike action. You take a sample of 50 voters. Assume this to be a binomial distribution. What is the standard deviation for this distribution?
A) 45
B) 4.5
C) 2.12
D) 20.25

Question

Quizplus · Accepted Answer

The probability of a vote in favor of the strike is 0.9. 
The probability of a vote against the strike is 1 - 0.9 = 0.1. 
The mean, or expected value, of the distribution is: μ = np = 50 x 0.9 = 45. 
The variance of the distribution is: σ^2 = np(1-p) = 50 x 0.9 x 0.1 = 4.5. 
Therefore, the standard deviation is the square root of the variance: σ = sqrt(4.5) ≈ 2.12.

Tabulation of a Strike Vote Showed That 90% of Those