Understanding the Question This may not be the actual way that the US government prepares the CPI, but it will provide a comparison.
You can set up a proportion. The base number for the CPI is 38.8 in 1970. That number (38.8) has more than doubled to get to 82.4, which also tells us that there was inflation. What your parents and grandparents bought in 1970 went to double the amount in 1980. Gasoline certainly did that.
Givens CPI in 1970 = 38.8 CPI in 1980 = 82.4 Eggs 1970 = 0.25 Edgs 1980 = X
Formula substitution and solution CPI 1970 / CPI 1980 = cost of eggs 1970 / cost of eggs 1980 38.8/82.4 = 0.25 / x Cross multiply 38.8 * x = 0.25 * 82.4 38.8 * x = 20.625 x = 20.628 /38.8 x = 0.53 dollars of 53 cents.
53 cents in 1980 which is slightly double as predicted.
Footnote As a matter of interest, my wife tells me that eggs now cost about 3.58 where we live. That's almost 7 times as expensive as they were in 1980. Something to think about. By the way, the price quoted is in Canada.
