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11) Calculate dist

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11) Calculate dist

by ern5231 » Sat May 15, 2010 10:15 pm
A Semicircle is divided into 8 portions and has the points O to W. The semi circle has the length of 1 mile and a man starts at O travelling at 15 mph. In between what points will the man be after 3 minutes?

A. Q to R B. R to S C. S to T D. T to U E. U to V
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by akdayal » Sat May 15, 2010 10:25 pm
it should be E
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by dkumar.83 » Sat May 15, 2010 10:37 pm
The circumference of the semicircle is (pi*r), which equals (pi*1/2) miles. Assuming pi=3. the distance comes to a little over 1.5 miles.
In 3 min the person would be covering a little over 3/4th of a mile (0.75 mile). This distance will be a little less than half of the distance calculated. hence the answer should be "B"; R to S.
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by Gmat_War » Sat May 15, 2010 10:45 pm
the semicircle has a length of 1 mile and it is divided into 8 equal parts.So each part will equal to 1/8=0.125 mile
The speed of the man is 15mph.
Thus in 60 minutes it goes 15 miles.
Hence in 3 minutes it will go (15/60)*3=0.75 miles
If OP=0.125,OQ=0.250,OR=0.375,OS=0.5,OT=0.625,OU=0.750
So at 3 minutes,he will be at point U
=>After 3 minutes he will be between U and V,that is option E
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by dkumar.83 » Sat May 15, 2010 11:07 pm
one question: what does the length of semicircle mean?

1. is it pi*r ?
2. or is it (pi*r+diameter) ?
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by indiantiger » Sun May 16, 2010 4:48 am
I have assumed that length means circumference of the semicircle = 1 mile
8 equal partitions are
o-p,p-q,q-r,r-s,s-t ,t-u,u-v,v-w
Now each is equal to 1/8 of a mile.

to cover one of the partitions it will take 1/8/(15) = 60/8*15 = 4/8 = 1/2 minute
time taken to cover o-p = 1/2
p-q =1/2 (total time =1)
q-r = 1/2 (total time =1.5)
r-s= 1/2 (total time = 2.0)
s-t = 1/2(total time = 2.5)
t-u = 1/2(total time = 3.0)
u-v (person will be here at the starting point that is u) (E)
v-w
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by Stuart@KaplanGMAT » Sun May 16, 2010 9:09 am
ern5231 wrote:A Semicircle is divided into 8 portions and has the points O to W. The semi circle has the length of 1 mile and a man starts at O travelling at 15 mph. In between what points will the man be after 3 minutes?

A. Q to R B. R to S C. S to T D. T to U E. U to V
Hi,

I'm not sure from where you got this problem, but you'll never see something this poorly worded in the GMAT.

First, what does "length" of the semi-circle mean? Circumference of the arc? Diameter? Radius? Circumference of the arc plus the diameter?

Second, nowhere does it say that the 8 portions are equal or where the points are located; are they all located on the arc? Are some of them located on the diameter?

Without clarification, there's no way to answer the question.

What's the source of the question?
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by dkumar.83 » Sun May 16, 2010 10:33 am
Hey stuart,

I totally agree, and that is the reason i am highly confused. I have got this from a friend of mine. Maybe its incorrect.

Thanks anyways.
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