BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

about its longest side as axis

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

about its longest side as axis

by sanju09 » Thu Nov 28, 2013 11:30 pm
A triangle of dimensions 6, 8, and 10 is rotated about its longest side as axis. Which of the following is nearest to the curved surface area of the solid so generated?
A. 120
B. 150
C. 180
D. 210
E. 240


Made Up

An example situation to the question is this figure.

Courtesy https://gknowledgecbse10.blogspot.in

Image
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 490
Joined: Thu Jul 04, 2013 7:30 am
Location: Chennai, India
Thanked: 83 times
Followed by:5 members

by Uva@90 » Fri Nov 29, 2013 5:16 am
Hi Sanju09,
Is Answer D ?

Regards,
Uva
Known is a drop Unknown is an Ocean
Top
Master | Next Rank: 500 Posts
Posts: 447
Joined: Fri Nov 08, 2013 7:25 am
Thanked: 25 times
Followed by:1 members

by Mathsbuddy » Fri Nov 29, 2013 8:56 am
The maximum radius is R = 4.8 (see diagram).

The curved surface area of a cone is pi * R * L where L = slant height.

We have 2 cones:

So total surface area = pi * R * (L1 + L2)
= 3.14 * 4.8 * (6 + 8) = 211 (approx.)

Answer = (D)
Attachments
Cones.png
Top
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Fri Nov 29, 2013 11:36 pm
Please draw on your own according to the following explanation:

∆ABC has AB = 6, BC = 10, and CA = 8, and consequently it is right angled at A. Mathsbuddy did justice to the situation that I described in the question. Now drop perpendicular from A on BC to meet BC in D. This AD would serve as the common radius in the resulting solid so generated. Area of ∆ABC is ½ AB.AC = ½ BC.AD = 24, hence AD = 4.8; for approximation purposes we'll later on take AD = 5.

The curved surface area of a cone = π (Base Radius) (Slant Height)

[Let's take π = 3 only]

The collective curved surface area of the solid so generated would equal

π(5)(6) + π(5)(8) = [spoiler]90 + 120 = 210. It's D.[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Post new topic Post Reply
• Page 1 of 1