Because of relatively high interest rates, most consumers attempt to pay off their credit card bills promptly. However, this is not always possible. An analysis of the amount of interest paid monthly...

Because of relatively high interest rates, most consumers attempt to pay off their credit card bills promptly. However, this is not always possible. An analysis of the amount of interest paid monthly by a bank’s Visa card holders reveals the amount is normally distributed with a mean of $27 and a standard deviation of $7.

What proportion of the bank’s Visa cardholders pay less than $15 in interest?