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Use a normal approximation to find the probability of the indicated number of voters.
In this case, assume that 124 eligible voters aged 18-24 are randomly selected.
Suppose a previous study showed that among eligible voters aged 18-24, 22% of them voted.
Find the probability that exactly 30 voted
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This problem is on Binomial distribution
n = 124 total trials; p = 0.22 is the probability of an individual success;
k = 30 is the number of successful trials.
Since the number of trials is great, we use the normal distribution as an approximation.
The mean is m = n*p = 124*0.22 = 27.28; the standard deviation is
SD = = = 4.61285 (rounded).
Now you can use your calculator
p = normalcfd( 29.5, 30.5, 27.28, 4.61285) = 0.0726 (rounded). ANSWER
The numbers 29.5 and 30.5 come with the continuity correction.
Solved.