A rectangular piece of iron sheet measuring 50 cm by 100 cm is rolled into a cylinder of height 50 cm. If the cost of painting the cylinder is Rs. 50 per square metre, then what will be the cost of painting the outer surface of the cylinder ?

The sheet when rolled has height = 50 cm and circumference = 100 cm, so the curved (outer) surface area = circumference × height = 100 cm × 50 cm = 5000 cm². Using the cylinder lateral-area relation (circumference × height = 2πrh) supports this approach. Convert 5000 cm² to m²: 5000/10,000 = 0.5 m² (unit conversion follows from standard metric linear-to-area scaling). At Rs. 50 per m² the painting cost = 50 × 0.5 = Rs. 25. Hence option 1 (Rs. 25.00) is correct.