A 10-by-6 inch piece of paper is used to form the lateral surface of a cylinder. If the entire piece of paper is used to make the cylinder, which of the following must be true of the two possible cylinders that can be
formed?
A The volume of the cylinder with height 10 is 60/p cubic inches greater than the volume of the cylinder with
height 6.
B The volume of the cylinder with height 6 is 60/p cubic inches greater than the volume of the cylinder with
height 10.
C The volume of the cylinder with height 10 is 60p cubic inches greater than the volume of the cylinder with
height 6.
D The volume of the cylinder with height 6 is 60p cubic inches greater than the volume of the cylinder with
height 10.
E The volume of the cylinder with height 6 is 240/p cubic inches greater than the volume of the cylinder with
height 10.
OE B
Can Anyone explain me the reasoning?
I have doubts in it.
700+ Level Question
This topic has expert replies
-
- Master | Next Rank: 500 Posts
- Posts: 152
- Joined: Fri Apr 24, 2015 1:39 am
- Location: Rourkela Odisha India
- Thanked: 2 times
- Followed by:3 members
- GMAT Score:650
-
- Master | Next Rank: 500 Posts
- Posts: 363
- Joined: Sun Oct 17, 2010 3:24 pm
- Thanked: 115 times
- Followed by:3 members
Dimension of paper = 10 x 6akash singhal wrote:A 10-by-6 inch piece of paper is used to form the lateral surface of a cylinder. If the entire piece of paper is used to make the cylinder, which of the following must be true of the two possible cylinders that can be
formed?
A The volume of the cylinder with height 10 is 60/p cubic inches greater than the volume of the cylinder with
height 6.
B The volume of the cylinder with height 6 is 60/p cubic inches greater than the volume of the cylinder with
height 10.
C The volume of the cylinder with height 10 is 60p cubic inches greater than the volume of the cylinder with
height 6.
D The volume of the cylinder with height 6 is 60p cubic inches greater than the volume of the cylinder with
height 10.
E The volume of the cylinder with height 6 is 240/p cubic inches greater than the volume of the cylinder with
height 10.
OE B
Can Anyone explain me the reasoning?
I have doubts in it.
To form a cylinder from this we have 2 ways:
1) height = 6 and circumference = 10; 2*pi*r1 =10, r1 = 5/pi
2) height = 10 and circumference = 6; 2*pi*r2 = 6, r2 = 3/pi
Volume of cylinder = pi * r^2 * h
1) volume when height is 6 = pi * (5/pie)^2 * 6 = 150/pi
2) volume when height is 10 = pi * (3/pie)^2 *10 = 90/pi
Thefore the volume when height is 6 is (150-90)/pi = 60/pi greater than the volume when height is 10
ans = b
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Here are two related questions involving cylinders:
https://www.beatthegmat.com/a-cylindrica ... 71714.html
https://www.beatthegmat.com/solid-geomet ... 29356.html
Cheers,
Brent
https://www.beatthegmat.com/a-cylindrica ... 71714.html
https://www.beatthegmat.com/solid-geomet ... 29356.html
Cheers,
Brent
-
- Master | Next Rank: 500 Posts
- Posts: 137
- Joined: Fri Nov 13, 2015 11:01 am
- Thanked: 1 times
- Followed by:2 members
Hi Brent,
I am little confused about this question because my answers yield to the 60pi not 60/pi; ei: D
here is how i did it; please tell me what i did wrong.
case1, H=6 , R=5
since volume of a cylinder is pi x r^2 x H
volume = 150pi
case2: H=10, R=3
volume= 90pi
Hence case 1 is greater than case 2 by 60pi
please explain to me what i did wrong here.
I am little confused about this question because my answers yield to the 60pi not 60/pi; ei: D
here is how i did it; please tell me what i did wrong.
case1, H=6 , R=5
since volume of a cylinder is pi x r^2 x H
volume = 150pi
case2: H=10, R=3
volume= 90pi
Hence case 1 is greater than case 2 by 60pi
please explain to me what i did wrong here.
Brent@GMATPrepNow wrote:Here are two related questions involving cylinders:
https://www.beatthegmat.com/a-cylindrica ... 71714.html
https://www.beatthegmat.com/solid-geomet ... 29356.html
Cheers,
Brent
-
- GMAT Instructor
- Posts: 2630
- Joined: Wed Sep 12, 2012 3:32 pm
- Location: East Bay all the way
- Thanked: 625 times
- Followed by:119 members
- GMAT Score:780
The issue is that your sheet of paper's dimensions become the height and the circumference of the cylinder's base, not the radius of the cylinder's base. (Roll a piece of paper into a cylinder and you can see why this is.) You're using 5 and 3 as possible radii when 10 and 6 should represent possible circumferences, yielding radii of 5/Ï€ and 3/Ï€, respectively. Everything else is right though, so your geometry is on the right track!Amrabdelnaby wrote: case1, H=6 , R=5
since volume of a cylinder is pi x r^2 x H
volume = 150pi
case2: H=10, R=3
volume= 90pi