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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]
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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]
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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



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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.
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Harsha
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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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