SOLUTION: The Better Business Bureau settles 75% of complaints it receives involving new car dealers. Suppose a sample of 160 complaints involving new car dealers is selected. Find the pr

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Question 1124583: The Better Business Bureau settles 75% of complaints it receives involving new car dealers. Suppose a sample of 160 complaints involving new car dealers is selected.
Find the probability that Better Business Bureau settles less than 129 of these complaints.

Answer by rothauserc(4718)   (Show Source): You can put this solution on YOUR website!
mean is 0.75
:
we do not know the standard deviation of the population, so we will use the standard error
:
standard error = square root(0.75 * (1-0.75) / 160) = 0.0342
:
the sample size is greater than 30, so we can use the normal distribution
:
129/160 is approximately 0.8062
:
we want the probability that X is less than 0.8062
:
z-score = (0.8062 - 0.75)/0.0342 is approximately 1.64
:
using table of z-scores, we find the probability associated with z-score of 1.64
:
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Probability ( X < 0.8062 ) = 0.9495
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