Squares

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

by kanha81 » Fri Jun 05, 2009 10:11 am

Please explain your answer for the attached question.

What I am having difficulty understanding is the easier way of calculating the Perimeter of the square.

I know it is 4s, but with the figure attached, I was not able to calculate within the 2 mins time frame.

Thanks a bunch

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Source: Beat The GMAT — Problem Solving | Fri Jun 05, 2009 10:11 am

ssmiles08: Master | Next Rank: 500 Posts; Posts: 472; Joined: Sun Mar 29, 2009 6:54 pm; Thanked: 56 times

by ssmiles08 » Fri Jun 05, 2009 10:22 am

I got 7/3 as my answer:

perimeter is not 4s it is 14s. You are counting the whole squares. you need to count the sides of the figure as a whole

6s^2 = 14s

6s^2 - 14s = 0

2s(3s -7) = 0

s = 7/3

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

by kanha81 » Fri Jun 05, 2009 10:33 am

ssmiles08 wrote:I got 7/3 as my answer:

perimeter is not 4s it is 14s. You are counting the whole squares. you need to count the sides of the figure as a whole

6s^2 = 14s

6s^2 - 14s = 0

2s(3s -7) = 0

s = 7/3

What I meant was that perimeter of 1 square is 4s, not all the 6 squares. I still don't understand how you got 14s.
Shouldn't the Perimeter be calculated as?
6*(4s) - shared sides = 24s - 10s ? How do you deduce 10s?

Apologies for the slower brain activity...

Want to Beat GMAT.
Always do what you're afraid to do. Whoooop GMAT

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gmahendru: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Sun Mar 30, 2008 2:50 am; Thanked: 2 times

by gmahendru » Fri Jun 05, 2009 11:30 am

@kanha...

it is perimeter.. y you are subtracting shared sides... just add outer sides and those are 14 in nos...

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ssmiles08: Master | Next Rank: 500 Posts; Posts: 472; Joined: Sun Mar 29, 2009 6:54 pm; Thanked: 56 times

by ssmiles08 » Fri Jun 05, 2009 12:18 pm

kanha81 wrote:
ssmiles08 wrote:I got 7/3 as my answer:

perimeter is not 4s it is 14s. You are counting the whole squares. you need to count the sides of the figure as a whole

6s^2 = 14s

6s^2 - 14s = 0

2s(3s -7) = 0

s = 7/3
What I meant was that perimeter of 1 square is 4s, not all the 6 squares. I still don't understand how you got 14s.
Shouldn't the Perimeter be calculated as?
6*(4s) - shared sides = 24s - 10s ? How do you deduce 10s?

Apologies for the slower brain activity...

Ok lets start with the top square and work our way clockwise:

1st square has 3 outer boundary sides: 3s
2nd square has only 2 outer boundary sides: 2s
3rd square has 3 outer boundary sides: 3s
4th square has only 1 outer side: 1s
5th square has 3 outer boundaries: 3s
6th square has 2 outer sides: 2s

3+2+3+1+3+2 = 14s

perimeter is just the outer boundary of a figure as a whole. I think you are adding 3 more sides (which are shared by the other squares).

Hopefully that clarifies a it a little.

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