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# A car traveling at a certain constant speed takes 2 seconds

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Senior Manager
Joined: 10 Mar 2008
Posts: 343
A car traveling at a certain constant speed takes 2 seconds [#permalink]

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23 Sep 2008, 07:00
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5

Could you please explan using RTD chart. I'm messing up the conversions for some reason. Thanks!
SVP
Joined: 07 Nov 2007
Posts: 1761
Location: New York

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23 Sep 2008, 07:23
vksunder wrote:
A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5

Could you please explan using RTD chart. I'm messing up the conversions for some reason. Thanks!

D=RT

R= 75 km/hr = 75 /60*60 KM/sec
D= 1 km

T= D/R = 60*60/75 = 48sec

-----------

T2= 48+2= 50
R2*T2=D

R2= 1/50 km/se = 60*60/50 km/hr = 72

B
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Director
Joined: 23 May 2008
Posts: 757

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23 Sep 2008, 21:58
in the RTD chart I got

R*T=D
1) x*(t+2/3600)=1
2) 75*t=1, so t=1/75

sub t into equation 1
x(1/75 +2/3600) =1 x=72
Re: Distance   [#permalink] 23 Sep 2008, 21:58
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# A car traveling at a certain constant speed takes 2 seconds

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