A restaurant sells two round pizzas whose diameters are in the ratio 2 : 3. The smaller one is priced at ₹240. If the price is to be strictly proportional to the amount of pizza, what should the larger one cost?

The amount of pizza goes with the area, and areas of circles are in the ratio of the squares of the diameters: $(3/2{)}^2=9/4$. So the price = $240\times 9/4=$ ₹540. The trap ₹$360=240\times 3/2$ scales by the linear ratio, the everyday intuition that a pizza half again as wide holds half again as much; ₹720 multiplies by 3; ₹$1080=240\times 9/2$ squares the 3 but not the 2.