:9. Solution. Since (600-500)/100 = 100/100 = 1, and
(665-500)/100 = 165/100 = 1.65, the desired percentage is
approximately equal to the area under the normal curve between 1
and 1.65. The area under the normal curve between 0 and 1.65 is
about one-half of 90%, or 45%. The area under the normal curve
between 0 and one is about one-half of 68%, or 34%. The area
under the normal curve between 1 and 1.65 is 45 - 34 = 11%. The
closest of the choices is 10%.