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Answer:
78.88% probability that this sample proportion is within 0.05 of the population proportion
Step-by-step explanation:
We need to understand the normal probability distribution and the central limit theorem to solve this question.
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 normally distributed random variable X, with mean and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
For proportion p in a sample of size n, we have that
In this question:
So
What is the probability that this sample proportion is within 0.05 of the population proportion.
This is the pvalue of Z when X = 0.8 + 0.05 = 0.85 subtracted by the pvalue of Z when X = 0.8 - 0.05 = 0.75.
X = 0.85
By the Central Limit Theorem
has a pvalue of 0.8944.
X = 0.75
has a pvalue of 0.1056.
0.8944 - 0.1056 = 0.7888
78.88% probability that this sample proportion is within 0.05 of the population proportion