Posted by **Mary** on Sunday, March 27, 2011 at 7:30pm.

If the cost of a cell phone has decreased 400% during the past 10 years, does that correspond to a decrease of four times?

- math -
**PsyDAG**, Monday, March 28, 2011 at 11:56am
To me, without more data, it doesn't make sense. A decrease of 100% would mean it costs nothing.

If the rate of decrease was constant over the 10 years, it would mean a decrease of 40% each year. Assuming it cost $100 originally:

$100

$60

$36

$21.60

$12.96

$7.78

That is only after 5 years!

Sorry that I cannot be of more help.

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