Mr. Roper cuts his lawn 15 days a month beginning in April and ending in September. From October to the end of March he cuts his lawn three times a month. What is the average number of times that Mr. Roper cuts his yard per month? Let's answer step by step:
For 6 months of the year he cuts his yard 15 days per month so he cuts his yard 6 * 15 = 90 times. For the remaining 6 months of the year, he cuts his yard three times a month so he cuts his yard 6 * 3 = 18 times. He cuts his yard 90 times for part of the year and 18 times for the rest of the year for a total of 90 + 18 = 108 times. There are 12 months in a year and he cuts his yard 108 times so he averages 108 / 12 = 9 times per month. The answer: 9.