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# Speed problem in gmatprep1

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Intern
Joined: 13 Jul 2009
Posts: 6

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13 Jul 2009, 09:26
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Hi
This problem appeared in gmatprep1
Distance travlled by a boat upstream is 90 miles and speed is v-3 miles/hr.While going downstream boat has a speed of v+3 miles/hr.If distance travelled upstream and downstream is same and boat takes 1/2 hr more to travle upstream than time for downstream,what is the downstream time?
Thanks
Intern
Joined: 05 Sep 2006
Posts: 14
Re: Speed problem in gmatprep1 [#permalink]

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13 Jul 2009, 11:35
Here's the solution..
Upstream ( d=90, s = (v-3), t=t1 ) , since $$S = D/T$$ or $$T = D/S$$ therefore $$t1 = 90/(v-3)$$
Downstream ( d=90, s=(v+3), t=t2 ) , $$t2=90/(v+3)$$

As per the problem, $$t1=t2+ 1/2$$ or $$t1-t2=1/2$$
therefore

$$(90/(v-3)) -(90/(v+3)) = 1/2$$
Solving this equation we get v = 33
substituting the value of V in the equation for downstream we get $$t2 = 90/(30+3)= 2.5$$
Re: Speed problem in gmatprep1   [#permalink] 13 Jul 2009, 11:35
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