The line graph below shows US consumers' average annual expenditures on cell phone and residential phone services between 2001 and 2010.

The line graph compares the annual expenditure average on residential and mobile phone services in the years 2001 and 2010 in the United States.

Overall

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, the chart shows two different curves, on one of them the cell phone lines and on the other, the residential services.

By contrast

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, the lines on the chart have opposite tendencies. Looking at the information in detail, we can see that mobile lines have increased from 200 to 800 dollars in only 9 years

while

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the residential figures have decreased by 300 dollars at the same time. Both curves are not perfectly stable and

thus

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, we notice some slight variations in 2002 and 2007.

Then

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, we observe an interesting aspect based on the fact that the line variations have had a very similar aspect in the sense they have behaved in exactly the reversed way to each other and had their axe in the year 2006. So, a drop in prices of residential phone services arrived at the same time as the rise of cell phones.