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

[BTGmoderatorLU]

Source: GMAT Paper Tests

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 (arithmetic mean) annual increase in the index over this period?

A. (x+100)/18
B. x/18
C. (100-x)/18
D. (x-100)/18
E. 100x/18

The OA is D

[Scott@TargetTestPrep]

Source: GMAT Paper Tests

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 (arithmetic mean) annual increase in the index over this period?

A. (x+100)/18
B. x/18
C. (100-x)/18
D. (x-100)/18
E. 100x/18

The OA is D

Solution:

The average (arithmetic mean) annual increase in the index over this period is:

(Change in price index) / (Change in years)

= (x - 100) / (1985 - 1967)
= (x - 100) / 18

Answer: D