# Aptitude - Volume and Surface Area - Discussion

Discussion Forum : Volume and Surface Area - General Questions (Q.No. 8)
8.
The slant height of a right circular cone is 10 m and its height is 8 m. Find the area of its curved surface.
30 m2
40 m2
60 m2
80 m2
Explanation:

l = 10 m,

h = 8 m.

So, r = l2 - h2 = (10)2 - 82 = 6 m.

Curved surface area = rl = ( x 6 x 10) m2 = 60 m2.

Discussion:
11 comments Page 1 of 2.

Akhil said:   4 years ago
@Mustafa.

It is a right circular cone. So given details are height 8 cm, slant height 10 cm, we need to find the base length ie the radius, which can be obtained Pythagoras theorem.
(1)

Ngawang Chojey said:   6 years ago
@Nikita is right.

You can use the formula of a right triangle to derive the length of base i.e. equal to radius: h^2=a^2+b^2.

Where, h=slant height, a=hight of a right triangle and b=base of a right triangle.
(1)

Nikita said:   7 years ago
L = 10 m.
H = 8 m.
R = (10 * 10) - (8 * 8).
R = 100 - 64 = 36.
Square root of 36 is 6.
= 6 * 10 = 60m.

Mustafa said:   7 years ago
Yeah, 10-8 should be 2 not 6.
(1)

Justin said:   7 years ago
Answer is A, why you are taking as a full height of 10?

I think;
(22/7) x 6 x 5,
(22/7) x 30 => is a correct Answer.
(1)

Gowtham said:   7 years ago
@Sunil.

How 10-8 = 6?

It should be 2.
(1)

Krutarth vaidya said:   8 years ago
C is also correct.

L = 10,

H = 8,

So, r = l2 - h2 = (10)2 - 82 = 6 m.

Area = 60 m^2.

Islam said:   8 years ago
C is correct.

l = 10 m,

h = 8 m.

So, r = l2 - h2 = (10)2 - 82 = 6 m.

Curved surface area = rl = ( x 6 x 10) m2 = 60 m2.

Subhasis said:   8 years ago
I think r should be 6/2 = 3.

Sunil said:   8 years ago
Curved surface area of cone = rl.

l stands for slant height.

r = ?
height = 8 m.
l = 10 m.

First we should find to r (radius). Then we can find curved surface area of cone.

r = l - r.
r = 10-8 = 6 m.

Put value of r in given formula.

rl = 6 m*10 m = 60 m^2.

(C) 60 m^2 correct option.