Question

From 1980 to 1990, the consumer price index (CPI) increased from 82.4 to 130.7. If a gallon of apple juice cost $0.95 in 1980 and the price of apple juice increased at the same rate as the CPI from 1980 to 1990, approximately how much did a gallon of apple juice cost in 1990?

Answer 1

Use a proprtion.

\( \dfrac{CPI~1980}{CPI~1990} = \dfrac{price~in~1980}{price~in~1990}\)