GMAT PREP DS Question

[sindhujah_kk]

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

1) The car travelled the first 200 km in 2.5 hrs.

2) If the car's average speed had been 20km/hr greater than it was it would have travelled 400km in 1 hr less time than it
did.


Ans: B

Can someone explain me this question.[/list][/list]

[kmittal82]

1) Is not enough, since the card couldve travelled the remaining 200km in a variety of hours.

2) Let total time taken to travel 400km = x

Thus, average speed = 400/x km/hr

>If the car's average speed had been 20km/hr greater than it was
= (400/x) + 20

Time taken to cover 400km with that speed -> 400/[(400/x) + 20]

> than it was it would have travelled 400km in 1 hr less time than it
did.

400/[(400/x) + 20] = x - 1

You now have one equation and you can solve for x to answer the question.

[selango]

D=400 km,T=?

stmt1,

We dont know the car speed for next 200 kms.

In suff

stmt2,

400/S=T

400/S+20=T-1

s+20/400=1/T-1

1/T+1/20=1/T-1

1/T-1-1/T=1/20

From this you can find T value.

Suff

Pick B