Åk 6–9
 
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4.3 Percent Change
When several changes in percent happen one after each other, it is much easier if you can use a rate of change.

A computer costs 8,000 kr.  The price increases first by 20 % and then decreases by 10 %.  What does the computer cost?

After the price increase the computer costs:



Foto: Fredrik Hjelm



100 % + 20 % = 120 % = 1.20
1.20 · 8,000 kr = 9,600 kr


After the price decrease, you will pay 100 % - 10 % = 90 % of the price 9,600 kr.



0.90 · 9,600 kr = 8,640 kr


The rate of change for the increase is 1.20.
The rate of change for the decrease is 0.90.



The total rate of change is 1.20 · 0.90 = 1.08

The new price is then 1.08 · 8,000 kr = 8,640 kr