Using the Empirical Rule, it is found that 99.7% of his commutes will be between 9 and 33 minutes.
It states that, for a normally distributed random variable:
In this problem, considering a mean of 21 minutes and a standard deviation of 4 minutes, we have that:
Within 3 standard deviations of the mean, hence, 99.7% of his commutes will be between 9 and 33 minutes.
More can be learned about the Empirical Rule at https://brainly.com/question/24537145
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