From 1940 to 1980 the consumer price index (CPI) increased from 28.6 to 89.4. If a gallon of milk cost $0.75 in 1940 and the price of milk increased at the same rate as the CPI from 1940 to 1980, approximately how much did a gallon of milk cost in 1980?

I need help getting this started. can someone help me? :)

Question

From 1940 to 1980 the consumer price index (CPI) increased from 28.6 to 89.4. If a gallon of milk cost $0.75 in 1940 and the price of milk increased at the same rate as the CPI from 1940 to 1980, approximately how much did a gallon of milk cost in 1980? 

I need help getting this started. can someone help me? :)

mertsj · Answer

Write a proportion.

mertsj · Answer

$$\frac{28.6}{89.4}=\frac{.75}{x}$$

anonymous · Answer

I may be wrong, but it looks like it's asking for the rate in change over the past forty years.
Then multiply that by the cost of milk to arive at the adjusted price in 1980

mertsj · Answer

Cross multiply and solve.

anonymous · Answer

Thank you, :)

anonymous · Answer

well, I don't think this is a division problem, more of a subtration

anonymous · Answer

1980-1940 = 40 years
89.4 - 28.6 = 60.80

anonymous · Answer

now you could do your division 60.80/40= 1.52
and multiply that by the cost of milk in 1940
0.75 * 1.52 =$1.14

anonymous · Answer

Thank you! I was doing that but somewhere I got the wrong answer! Thank you! :)

anonymous · Answer

and if that is not the answer then I might think to add the 1.52 to the 0.75 =$2.27