Question

The radii of two right circular cylinders are in the ratio 3 ∶ 4 and heights are in the ratio 4 ∶ 5. The ratio of their curved surface areas is:
1. 3 ∶ 5
2. 2 ∶ 5
3. 2 ∶ 3
4. 1 ∶ 3

Answer 1

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