Question: A special balloon increases by two-fifths of its previous volume every hour when placed under water. If its original volume is 500cm, 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 500cm which is (2 / 5) * 500cm = 200cm. After the first hour, it will have a volume of (500 + 200)cm = 700cm. In the second hour, it will increase in volume by two - fifths of 700cm which is (2 / 5) * 700cm = 280cm. After the second hour, it's volume will be (700 + 280)cm = 980cm. So the answer is 980.