Question

@DebbieG

Answer 1

The CPI is really a "relative" price, so by saying that the price of tangerines increased at the same rate at the CPI, it's saying that the ratio of prices from 1960 to 1970 is the same as the ratio of the CPI from 1960 to 1970.

In other words:\[\Large \dfrac{ 1960~CPI }{ 1970~CPI }=\dfrac{ \text{tangerine price 1960}} { \text{tangerine price 1970} } \]

so if t= the 1970 price of tangerines,
\[\Large \dfrac{29.6}{ 38.8 }=\dfrac{0.31} { t } \]

Then solve that for t (cross-multiply and divide should work nicely).