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Answer:
11.70% probability that the mean outstanding credit balance exceeds $700
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal probability distribution
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean and standard deviation
, the zscore of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
Central Limit Theorem
The Central Limit Theorem estabilishes that, for a random variable X, with mean and standard deviation
, the sample means with size n of at least 30 can be approximated to a normal distribution with mean
and standard deviation
In this problem, we have that:
In an SRS of 100 couples, what is the probability that the mean outstanding credit balance exceeds $700?
This is 1 subtracted by the pvalue of Z when X = 700. So
By the Central Limit Theorem
has a pvalue of 0.8830
1 - 0.8830 = 0.1170
11.70% probability that the mean outstanding credit balance exceeds $700