Rates

[naveenhv]

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 time than it did.

[vikram4689]

This can be done in an oral manner.
a) it is insufficient, we do not know about next half of jouney.

b) B will give you an equation

400/s - 400/(s+20) = 1
From here you can find s and s = d/t = 400/t , so you can find t , hence sufficient. DO NOT SOLVE it is DS :)

[jnelson0612]

Nice work vikram!

[krishnan.anju1987]

Funny, how they put the trap in A. :) GMAT can get so tricky.

[RonPurewal]

Funny, how they put the trap in A. :) GMAT can get so tricky.

i wouldn't really call that a "trap". instead, i would call it a test of whether you are thinking the right way about these problems.

here's what i mean
if your approach is too "textbook" (as opposed to "thinking the way people think on planet earth"), then you may have a hard time with the first statement -- because, in school (which is totally not like planet earth), you usually assume that everything in the world happens at constant speed, forever. well, unless you are in calculus class, but there's no calculus on this exam.

on the other hand, if you are actually thinking about this problem like someone on planet earth, then your instant response to the first statement will be "dude, i have no idea what happens during the second half of the trip."

so, this problem is actually a nice wake-up call if you think the first statement is a trap. in that case, you should probably retool the entire way you think about word problems on this exam.

[krishnan.anju1987]

Actually I did not fall for that one. The moment I read the sentence I found that there is no info about the rest of the journey. But then back at school I remember I would have just continued solving the problem using that info. That's when I realized that unknowingly my approach to such problems have changed.

[RonPurewal]

Actually I did not fall for that one. The moment I read the sentence I found that there is no info about the rest of the journey. But then back at school I remember I would have just continued solving the problem using that info. That's when I realized that unknowingly my approach to such problems have changed.

good -- that means you've internalized a great deal of the right mentality for this exam. keep it up.