A set of data has a normal distribution with a mean of 180 and a standard deviation of 20. What percent of the data is in the interval 140 - 220?
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Explanation:
We are given the information that this distribution is normal with a mean
To answer the question, we will convert this problem into a standard normal distribution
Thus:
This tells us the interval we're being asked about is analogous to determining what percent of the standard normal distribution
In statistics there is a handy "rule of thumb" sometimes called the Empirical Rule which says the approximately 95% of the data in a normal distribution lies in the interval