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

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GMATT73
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Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 00:38
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Who will be the first to find the <2 minute trick??

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Re: Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 00:49
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
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Re: Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 01:03
Good one Dashiya :P

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.
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Re: Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 01:07
GMATT73 wrote:
Good one Dashiya :P


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 :lol: :lol: :lol:
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Re: Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 01:15
ps_dahiya wrote:
GMATT73 wrote:
Good one Dashiya :P


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 :lol: :lol: :lol:


OOps :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. It`s also where the samurais get their arrow tips sharpened.

Sorry about that, Dahiya.
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Re: Who will be the first to find the <2 minute trick?? [#permalink] New post   09 Jul 2006, 01:18
GMATT73 wrote:
ps_dahiya wrote:
GMATT73 wrote:
Good one Dashiya :P


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 :lol: :lol: :lol:


OOps :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. It`s where the samurais get their arrow tips sharpened.

Sorry about that, Dahiya.


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



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Re: Who will be the first to find the <2 minute trick?? [#permalink]
09 Jul 2006, 01:18
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