GMATPrep Question

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mpaudena: Senior | Next Rank: 100 Posts; Posts: 80; Joined: Wed Jun 04, 2008 1:16 pm; Thanked: 3 times

by mpaudena » Wed Oct 14, 2009 6:10 pm

How much time did it take a certain car to travel 400 kilometers?

(1) The car traveled the first 200 kilometers in 2.5 hours.

(2) If the car's average speed had been 20 kilometers per hour greater than it was, it would have traveled the 400 kilometers in 1 hour less ime Han it did.

The answer is B, I picked E. I just need to know how. Thanks in advance.

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Source: Beat The GMAT — Data Sufficiency | Wed Oct 14, 2009 6:10 pm

sanjana: Master | Next Rank: 500 Posts; Posts: 182; Joined: Sun Aug 02, 2009 7:19 pm; Thanked: 18 times; GMAT Score:680

by sanjana » Wed Oct 14, 2009 10:16 pm

We have RT=400
We need to find T.

Statement 1
-----------

Information is given only about the 1st 200 km. We have no information on how to find the time it took for the next 200,hence insufficient.

Statement 2
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Rate Time Distance

Actual r t 400
Virtual r+20 t-1 400

From this, since D is same

we have,rt=(r+20)(t-1)
rt=rt-r+20t-20
20t-r=20 -- (eqn1)

rt=400
r=t/400

Substitute this in eqn 1 and we can find t.
Hence B.

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