Question: 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? Think carefully first, then make a decision:
In the first hour, the balloon will increase in volume by two - fifths of 500cm³ which is (2 / 5) * 500cm³ = 200cm³. After the first hour, it will have a volume of (500 + 200)cm³ = 700cm³. In the second hour, it will increase in volume by two - fifths of 700cm³ which is (2 / 5) * 700cm³ = 280cm³. After the second hour, it's volume will be (700 + 280)cm³ = 980cm³. So the answer is 980.