beginners'bin#3

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

beginners'bin#3

by sanju09 » Thu Mar 25, 2010 11:50 pm

If the radius of a circle is increased by 20 percent, then what is the percent increase in its area?
(A) 40
(B) 44
(C) 120
(D) 144
(E) 150

[spoiler]OA B[/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

Source: Beat The GMAT — Problem Solving | Thu Mar 25, 2010 11:50 pm

rockeyb: Legendary Member; Posts: 537; Joined: Sun Jul 19, 2009 7:15 amFollowed by: 1 member; Location: Nagpur , India; Thanked: 41 times

by rockeyb » Fri Mar 26, 2010 1:42 am

Assume the radius = 100.

So new radius = 120 .

Difference in area = pai(100^2 - 120^2)

= pai(4400)

% increase = (difference/ Original ) x 100

=[ pai(4400)/pai(10000)]x100

[spoiler]% increase = 44% . B[/spoiler]

"Know thyself" and "Nothing in excess"

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Fri Mar 26, 2010 1:47 am

rockeyb wrote:Assume the radius = 100.

So new radius = 120 .

Difference in area = pai(100^2 - 120^2)

= pai(4400)

% increase = (difference/ Original ) x 100

=[ pai(4400)/pai(10000)]x100

[spoiler]% increase = 44% . B[/spoiler]

well, the bold part could have been otherwise

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

harshavardhanc: Legendary Member; Posts: 526; Joined: Sat Feb 21, 2009 11:47 pm; Location: India; Thanked: 68 times; GMAT Score:680

by harshavardhanc » Fri Mar 26, 2010 1:59 am

sanju09 wrote:If the radius of a circle is increased by 20 percent, then what is the percent increase in its area?
(A) 40
(B) 44
(C) 120
(D) 144
(E) 150

[spoiler]OA B[/spoiler]

Area proportional to R^2 .

So if R becomes 1.2R , R^2 becomes 1.44R^2 . Therefore, increase in area = 44 %. IMO B.

Regards,
Harsha

rockeyb: Legendary Member; Posts: 537; Joined: Sun Jul 19, 2009 7:15 amFollowed by: 1 member; Location: Nagpur , India; Thanked: 41 times

by rockeyb » Fri Mar 26, 2010 2:27 am

sanju09 wrote:
rockeyb wrote:Assume the radius = 100.

So new radius = 120 .

Difference in area = pai(100^2 - 120^2)

= pai(4400)

% increase = (difference/ Original ) x 100

=[ pai(4400)/pai(10000)]x100

[spoiler]% increase = 44% . B[/spoiler]
well, the bold part could have been otherwise

agreed my mistake . Thanks .

"Know thyself" and "Nothing in excess"

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