The number of coins 1.5 cm in diameter and 0.2 cm thick to be melted to form a right circular cylinder of height 10 cm and diameter 4.5 cm is

The ratio between the curved surface area and the total surface area of a right circular cylinder is 1 : 2. If the total surface area is 616 cm², then the volume of the cylinder is

In a cylinder, if the radius is halved and the height is doubled, then the volume will be

The radius of a wire is decreased to one-third. If volume remains the same, the length will become

The diameter of a roller, 1 m long, is 84 cm. If it takes 500 complete revolutions to level a playground, the area of the playground is