9. What is the area under the normal curve between z= 0.0 and z = -1.35? 10. The mean amount spent by a family of four on food is $800 per month with a standard deviation of $75. Assuming that the food costs are normally distributed, what is the probability that a family spends less than $610 per month? 11. The mean score of a college entrance test is 700; the standard deviation is 50. The scores are normally distributed. What percent of the students scored below 620? 12. A study of a company's practice regarding the payment of invoices revealed that an invoice was paid an average of 21 days after it was received. The standard deviation equaled three days. Assuming that the distribution is normal, what percent of the invoices were paid within 15 days of receipt? 13. The weight of cans of fruit is normally distributed with a mean of 1,000 grams and a standard deviation of 50 grams. What percent of the cans weigh 900 grams or less?