Marla - Speed

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Marla - Speed

by gmatrant » Tue Nov 13, 2007 3:08 am
Can you tell me if this approach is right. Is there any other way to solve this

1. x =48
y/48 + (40-y)/60 = (y+160)/240
If the speed is the same then 40/48
but since we dont know the value of y. Its not possible.

2. y=20
20/x + 20/1.25x = 44/1.25x
if same speed 40/x.
percentage change , x cancels out, hence B
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by simplyjat » Fri Jan 11, 2008 4:09 am
You got the correct answer by filling the values back.... Its correct and works well for GMAT...

I would rather go for a straighter approach....
For the first half of the journey; let t1, d1 and s1 be the time distance and speed, for second half t2, d2 and s2.
Now we know that s2 = 1.25s1 = 1.25 x....

And we have to find (t1+t2)/t3, where t3 is the time for whole journey at speed X....

(t1+t2)/t3 = (d1/x + d2/1.25X) / ( (d1 + d2) / x )
= ( d1 + 4*d2 ) / 5*( d1 + d2 )

for the ratio we have only d1 and d2 left as unknown... and we also know that d1 = y and d2 = 40 - y... and thus the ratio depends on the value y...
simplyjat