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# ds racing problem

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Manager
Joined: 05 Oct 2005
Posts: 200
ds racing problem [#permalink]

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12 Jul 2006, 15:59
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hello

plz explain your reasoning and equation used to come to the answer

thanks
How long did it take Bob to complete the race?
1.If Bob were 2/3 faster,his time would hav been 3
hrs.
2.Bob's average speed was 30miles per hr.
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Director
Joined: 06 May 2006
Posts: 791

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12 Jul 2006, 16:15
#1. If Bob were 2/3 faster then time would have been 3hrs.
=> If distance to be covered is constant, then speed varies inversely with time... v1/v2=t2/t1

We have v2 = (5/3)v1 and t2=3. Putting in the equation, we get t1 = 5 hrs

#2. Only speed is given, no distance. Insufficient.

Answer is A.
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Senior Manager
Joined: 07 Jul 2005
Posts: 404
Location: Sunnyvale, CA
Re: ds racing problem [#permalink]

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12 Jul 2006, 16:16
mand-y wrote:
:)hello

plz explain your reasoning and equation used to come to the answer

thanks
How long did it take Bob to complete the race?
1.If Bob were 2/3 faster,his time would hav been 3
hrs.
2.Bob's average speed was 30miles per hr.

(A)

Let original time taken = y
original speed = x

Orig distance = new distance

xy = x(1+2/3)3
y = 5
SVP
Joined: 30 Mar 2006
Posts: 1728

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13 Jul 2006, 00:07
A

1) Let Distance be D
Original Time be Y and speed be X

Hence D = XY

New speed = X +2X/3 = 5/3x

New time = 3
D/5X/3 = 3
3D/5x= 3
3XY /5x = 3
y = 5

2) Only speed given no other information hence not suff
13 Jul 2006, 00:07
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# ds racing problem

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