Correct Answer - Option 1 : 3 ∶ 5

**Given **

Ratio of radius = 3 : 4

Ratio of Heights = 4 : 5

**Formula Used **

Curved Surface area = 2 π R H (where R = radius, H = height)

**Calculation **

Let, the radii be 3x and 4x

and the heights be 4y and 5y [Where x and y are constant]

For 1st cylinder, radius = 3x, height = 4y

For 2nd cylinder, radius = 4x, height = 5y

Ratio of curved surface area(1st : 2nd) = 2π × 3x × 4y : 2π × 4x × 5y

⇒ 3 : 5

**∴ The required answer is 3 : 5 **