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# Who will be the first to find the <2 minute trick??

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Current Student
Joined: 29 Jan 2005
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Who will be the first to find the <2 minute trick??  [#permalink]  08 Jul 2006, 23:38
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Who will be the first to find the <2 minute trick??

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CEO
Joined: 20 Nov 2005
Posts: 2910
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
Followers: 20

Kudos [?]: 176 [0], given: 0

A

I got it in under 2 minutes using this:

Area of shaded region = PI/4*[x^2 - (x-1)^2+(x-2)^2-(x-3)^2+(x-4)^2]

Instead of squaring them directly and then calculating, I calculated like this:

There will be 5 x^2 terms and 3 will be +ve and 1 -ve.
x terms will be 2*(1-2+3-4) = -4
constant will be -1+4-9+16 = 10

Final area = PI/4 (x^2-4x+10)
So its A
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Current Student
Joined: 29 Jan 2005
Posts: 5239
Followers: 23

Kudos [?]: 257 [0], given: 0

Good one Dashiya

Alternatively, we could have just picked the numbers 10, 9, 8, 7, and 6 to represent the radius (x) and plugged it into the answer choices at the end:

100pi-81pi=19pi (area of outermost circle minus the band)

64pi-49pi=15pi (area of center circle minus the band)

36pi (area of innermost circle)

(36+15+19)pi=70pi/4

Substitute 10 for x in the answer choices and you will quickly discover that A is 70pi/4.
CEO
Joined: 20 Nov 2005
Posts: 2910
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
Followers: 20

Kudos [?]: 176 [0], given: 0

GMATT73 wrote:
Good one Dashiya

Hey MATT, I am noticing that for past many days you are writing my surname as Dashiya. Is it a typo or is it written in Japanese
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Current Student
Joined: 29 Jan 2005
Posts: 5239
Followers: 23

Kudos [?]: 257 [0], given: 0

ps_dahiya wrote:
GMATT73 wrote:
Good one Dashiya

Hey MATT, I am noticing that for past many days you are writing my surname as Dashiya. Is it a typo or is it written in Japanese

OOps Yep, "shi" is a syllable in the Japanese alphabet. Actually, "da-shi-ya" is the name of a storage house outside a shogun castle where archery weapons are kept. Its also where the samurais get their arrow tips sharpened.

CEO
Joined: 20 Nov 2005
Posts: 2910
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
Followers: 20

Kudos [?]: 176 [0], given: 0

GMATT73 wrote:
ps_dahiya wrote:
GMATT73 wrote:
Good one Dashiya

Hey MATT, I am noticing that for past many days you are writing my surname as Dashiya. Is it a typo or is it written in Japanese

OOps Yep, "shi" is a syllable in the Japanese alphabet. Actually, "da-shi-ya" is the name of a storage house outside a shogun castle where archery weapons are stored. Its where the samurais get their arrow tips sharpened.

If this is the case then I would prefer "da-shi-ya".
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

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