21 Suppose that the weekly use of gasoline for motor travel by adults in North Amenca is approximately normally distributed, with a mean of 16 gallons and a standard deviation of 5 gallons.

a) What proportion of adults use more than 20 gallons per week?

b) Find and interpret the lower and upper quarules and interquartile range of gasoline use.

c) Assuming that the standard deviation and the normal form would remain constant, to what level must the mean reduce so that only 5% use more than 20 gallons per week?

d) If the disu ibution of gasoline use is not actually nonnal. how would you expect it to deviate from normal"