from 1960 to 1970 the consumer price index increased from 29.6 to 38.8. If a dozen tangarines cost $0.31 in 1960 and the price of the tangerines increased at the rate as the CPI from 1960-1970 approximately how much did a dozen tangerines cost in 1970?

Question

nmspates · Answer

answer choices 
A $0.30
B $0.10
C $0.41
D $0.39

Vocaloid · Answer

the increase in price index is proportional to the increase in tangerines

you can set up a proportion where

(1970 tangerine price)/(1960 tangerine price) = (1970 consumer index)/(1960 consumer index) 
and solve for the 1970 tangerine price