A special balloon increases by two-fifths of its previous volume every hour when placed under water. If its original volume is 500cm³, what will its volume be after 2 hours underwater?
In the first hour, the balloon will increase in volume by two-fifths of 500cm^3 which is (2/5)*500cm^3 = 
<gadget id="calculator">2/5*500</gadget>
<output>200</output>
200cm^3.
After the first hour, it will have a volume of (500+200)cm^3 = 
<gadget id="calculator">(500+200)</gadget>
<output>700</output>
700cm^3.
In the second hour, it will increase in volume by two-fifths of 700cm^3 which is (2/5)*700cm^3 = 
<gadget id="calculator">2/5*700</gadget>
<output>280</output>
280cm^3.
After the second hour, it's volume will be (700+280)cm^3 = 
<gadget id="calculator">(700+280)</gadget>
<output>980</output>
980cm^3.

<result>980</result>