# Calculations based on Normal distribution

1 The distribution of purchase amounts of customers of a popular retail store is normal with a mean of $25 and a standard deviation of $8.

a. What percentage of customers spends less than $35?

b. What percentage of customers spends between $15 and $35?

c. Find the dollar amount such that 80% of customers spend at least this amount.

3. The lifetime of Kenless washing machines is normally distributed with a mean of 4 years. Only 15% of these machines last at least 5 years. What is the standard deviation of the lifetime of a Kenless washing machine?

4. Many drivers on US interstate highways do not observe the speed limit. Assume that the actual rates of speed driven in the US are normally distributed with a standard deviation of 5 miles per hour (mph).

If 20% of all US drivers travel at 65 mph or more, what is the average?

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#### Solution Summary

Calculations based on Normal distribution such as probability in an interval.