question 2

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bacali: Master | Next Rank: 500 Posts; Posts: 245; Joined: Thu Aug 16, 2007 12:41 pm

by bacali » Wed Nov 26, 2008 8:57 pm

On an aerial photograph, the surface of a pond appears as circular region of radius 7/16 inch. If a distance of 1 inch on the photograph corresponds to an actual distance of 2 miles, which of the following is the closest estimate of the actual surface area of the pond, in square miles?

A. 1.3
B. 2.4
C. 3.0
D. 3.8
E. 5.0

oa: b

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Source: Beat The GMAT — Problem Solving | Wed Nov 26, 2008 8:57 pm

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

Re: question 2

by sudhir3127 » Wed Nov 26, 2008 10:54 pm

bacali wrote:On an aerial photograph, the surface of a pond appears as circular region of radius 7/16 inch. If a distance of 1 inch on the photograph corresponds to an actual distance of 2 miles, which of the following is the closest estimate of the actual surface area of the pond, in square miles?

A. 1.3
B. 2.4
C. 3.0
D. 3.8
E. 5.0

oa: b

7/16th inch which is equal to 7/8miles in actual distance

thus surface area
pi* r^2

3* 49/ 64 ~ 2.4

thus B

hope that helps..

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bhumika.k.shah: Legendary Member; Posts: 941; Joined: Sun Dec 27, 2009 12:28 amFollowed by: 1 member; Thanked: 20 times

by bhumika.k.shah » Sat Jan 23, 2010 1:13 pm

Isnt the surface area of a circle =circumference of the circle= 2*pie*r?

And area of the circle = pie*r^2

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Sat Jan 23, 2010 6:07 pm

bhumika.k.shah wrote:Isnt the surface area of a circle =circumference of the circle= 2*pie*r?

And area of the circle = pie*r^2

no here perimeter of the pond will be circumference of a circle
but surface area will be the area of a circle

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bhumika.k.shah: Legendary Member; Posts: 941; Joined: Sun Dec 27, 2009 12:28 amFollowed by: 1 member; Thanked: 20 times

by bhumika.k.shah » Sat Jan 23, 2010 10:08 pm

how would it strike to me in the exam tht i need to take the area of a circle's formula to find the surface area instead of whaat i did by taking the circumference of a circle's formula..?
how would i know that the circumference in this case would be the perimeter of the pond ?

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djkvakin: Senior | Next Rank: 100 Posts; Posts: 84; Joined: Sat Oct 03, 2009 1:13 pm; Thanked: 11 times

by djkvakin » Sat Jan 23, 2010 11:01 pm

bhumika.k.shah wrote:how would it strike to me in the exam tht i need to take the area of a circle's formula to find the surface area instead of whaat i did by taking the circumference of a circle's formula..?
how would i know that the circumference in this case would be the perimeter of the pond ?

]Because circumference is the "perimeter" of the circle. The area is Pi*R^2.

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kunal_kc: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Tue Sep 02, 2008 12:33 am; Thanked: 2 times

by kunal_kc » Sat Jan 23, 2010 11:29 pm

i did the by the following way -:

first find the area: pie x 49/256

and then multiply by the area by 2 to get in miles, and my answer is coming A

comments please

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djkvakin: Senior | Next Rank: 100 Posts; Posts: 84; Joined: Sat Oct 03, 2009 1:13 pm; Thanked: 11 times

by djkvakin » Mon Jan 25, 2010 8:50 am

kunal_kc wrote:i did the by the following way -:

first find the area: pie x 49/256

and then multiply by the area by 2 to get in miles, and my answer is coming A

comments please

Since the area is in square units, you need to multiply the area by the factor of 2^2, not 2.
If you do this, you will get Pi * 49*4/256 = ~2.4

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kunal_kc: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Tue Sep 02, 2008 12:33 am; Thanked: 2 times

by kunal_kc » Mon Jan 25, 2010 5:36 pm

Thanks DJ, appreciate your help.

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Mon Jan 25, 2010 8:59 pm

bhumika.k.shah wrote:how would it strike to me in the exam tht i need to take the area of a circle's formula to find the surface area instead of whaat i did by taking the circumference of a circle's formula..?
how would i know that the circumference in this case would be the perimeter of the pond ?

FOR 2 D's figure that is triangle,square ,rect,rhom,paralleogram,circle......etc

circumference is perimeter
and surface area is nothing but area

for 3 D,s such as
cube , cuboid, spehere,cone,cylinder

we have surface area , lateral surface area , and volume

apart from that check the units perimeter/circumference=m,cm,km
area=m^2,cm^2
vol=m^3,cm^3

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