if price index for march is 107.9 how do I work out price of petrol
jan base month 100
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I'm guessing these are prices.
These are indices.
Jan base month price index 100
Price index for June 107.9
The question wants a price.
What is the price of petrol in June
The idea of a "Price Index" is to pick a point and call that the base, then adjust everything else to conform to that base.
Jan Price * (some factor) = Jan Index = 100
We just need to discover the "some factor".
In this case, division should be sufficient: 100/88.9 = 1.12486
You should now be able to use this factor to convert between prices and indeces based on January.
Price to Index
Mar 89.9 (multiply by 1.12486) ==> 101.1
May 94.8 (multiply by 1.12486) ==> 106.6
Index to Price
June 107.9 (divide by 1.12486) ==> 95.9
Note: I'm still just guessing in at least three places. If we don't yet match the book, you'll have to provide better information.