Question

The per capita consumption of coffee by people in the United States in a recent year was normally distributed, with a mean of 24.2 gallons and a standard deviation of 8.1 gallons.
What proportion of people in the U.S. drink more than 20 gallons of coffee a year?

Answer 1

Use z-scores.

Formula:
z = (x - mean)/sd

x = 20
mean = 24.2
sd = 8.1

Plug the values into the formula and calculate z. Then check a z-table using the z-score for the proportion of people who drink more than 20 gallons.

I hope this will help get you started.