If the consumer price index for a sample of goods and services purchased in Dallas rose from 100 at the end of 1967 to x at the end of 1985, what was the average Y (arithmetic mean) annual increase in the index over this period?  Choose the correct answer.
A) (x + 100)/18  B) x/18  C) (100 − x)/18  D) (x − 100)/18  E) 100x/18
CPI in end of 1967 = 100   CPI in end of 1985 = x   Number of years = 18   Average annual increase in CPI Y= (x-100)/18   Answer (x − 100)/18
<result>D</result>
If the consumer price index for a sample of goods and services purchased in Dallas rose from 100 at the end of 1967 to x at the end of 1985, what was the average Y (arithmetic mean) annual increase in the index over this period?