Question

The diameters of the two cones are equal. If their slant height be in the ratio 5 : 7, find the ratio of their curved surface areas.

• A. 25 : 7
• B. 25 : 49
• C. 5 : 49
• D. 5 : 7

Answer 1

The correct option is D 5 : 7

Let radius of the both the cone be x cm

Ratio of their slant height = 5 : 7

Let slant height of the first cone = 5y

Let slant height of the second cone = 7y
Curved surface area of the cone = $\pi$rl

The ratio of their curved surface area $=\frac{\pi x\times 5y}{\pi x\times 7y}=5:7$