Will Laurie get to the apartment building before Ernest if they both

IMO C

Both tell us that relative time to reach the building

I'll go with option C.

Assumptions: Laurie is not Flash from DC so his walking speed is not faster than taxi's speed.

Laurie and Ernest will reach the apartment together only if they travel for a same time period 'T' via subway and taxi respectively.
Apart from travelling by taxi, Laurie has to walk 3 blocks so the time taken to walk will be included in Laurie's total time taken.
Either ways Laurie won't reach the apartment before Ernest does.

Cheers!

IMHO we can not make this kind of assumptions. So the answer should be E

Are we not assuming here walking is slowest of all methods of transport, which may empirically be correct but an assumption GMAT usually discourages. Maybe I am missing the point where we can prove Laurie will be slower without assuming the time added by the walk.

Both of them would reach at the same time given they choose the same mode of transport.

Apart from travelling by taxi, Laurie has to walk 3 blocks so the time taken to walk will be included in Laurie's total time taken. Either ways Laurie won't reach the apartment before Ernest does.

Hence option C

Car speed is 'x' then subway speed is '2x' . If Laurie distance is 'y' then Ernest distance is 'y/2'
Time taken by Laurie time= y/2x + extra time to cover 3blocks(whatever it maybe, say 'z')= t+z (where, t=y/2x)
Time taken by Ernest = (y/2 )/x = y/2x = t

As, both started embarking at the same time, so, Ernest will reach earlier.
Hence, (1) & (2) together are sufficient.
Hope it helps

Car speed is 'x' then subway speed is '2x' . If Laurie distance is 'y' then Ernest distance is 'y/2'
Time taken by Laurie time= y/2x + extra time to cover 3blocks(whatever it maybe, say 'z')= t+z
Time taken by Ernest = (y/2 )/x = y/2t = t

You've already assumed that laurie has covered the full distance to the apartment building by subway y/2x . thus the addition of "time to cover 3 blocks walking", z, in y/2x + z actually implies that she got to the apartment at subway speed and then walked 3 blocks further). There is no way to solve this problem without assuming that laurie walks slower than the taxi. A reasonable assumption, but an assumption nonetheless.

Let the distance be D.

1) Time taken by Laurie is \((D/S) + Tb\) (S is speed of subway, Tb is time to walk 3 blocks, Also given that S = 2 * T, where T is the speed of Taxi). No info about Ernest hence insufficient

2) Time taken by Ernest is D*2/S*2 = D/S, No info about Laurie hence insufficient

Combining both, We can get the answer C

Hi I have one question, Eventhough Ernest is closer to apartment building, what if ernest is in opposite route to Laurie, and that route is full of traffic?


Laurie -----------2x-------------- Apartment-------------------x(but full of traffic)-----Ernest

Bunuel

I agree that logically the answer should be C,But don't you think 3 blocks create a little bit of ambiguity here .Hypothetically It could be 10 mtrs or 1 mile anything.Then don't you think it changes the answer.

If the distance is D, then shouldn't be the time time take by Laurie is (D - 3 blocks distance)/S + 3 block distance/ walking speed?

Target question: Will Laurie get to the apartment building before Ernest if they both embark at the same time?

Statement 1: Laurie will take the subway, which is twice as fast as a taxi, then she will walk 3 blocks.
No information about Ernest. Statement 1 is NOT SUFFICIENT

Statement 2: Ernest who is 2 times closer to the apartment building than Laurie will take a taxi to the building.
No information about Laurie. Statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Since we have no information about the Laurie's walking speed or the length of the 3 blocks, there are several conflicting scenarios that satisfy BOTH statements. Here are two:

Case a: Laurie's travel distance = 20 miles, and Ernest's travel distance = 10 miles.
The taxi's speed = 5 miles per hour, and the subway's speed = 10 miles per hour
time = distance/speed
So, Ernest's travel TIME = 10/5 = 2 hours

Laurie travels 10 miles by subway (at a speed of 10 miles per hour), and she walks the remaining 10 miles (at a speed of 1 mile per hour)
So Laurie's total travel TIME = 10/10 + 10/1 = 11 hours
In this case, the answer to the target question is NO, Laurie will NOT get to the apartment building before Ernest


Case b: Laurie's travel distance = 20 miles, and Ernest's travel distance = 10 miles.
The taxi's speed = 5 miles per hour, and the subway's speed = 10 miles per hour
time = distance/speed
So, Ernest's travel TIME = 10/5 = 2 hours

Laurie travels 10 miles by subway (at a speed of 10 miles per hour), and she walks the remaining 10 miles (at a speed of 20 miles per hour)
So Laurie's total travel TIME = 10/10 + 10/20 = 1.5 hours
In this case, the answer to the target question is YES, Laurie WILL get to the apartment building before Ernest

Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,
Brent

@Bunuel- I believe, answer should be changed to E. Already explained nicely by Brent above.

Shouldn't the time taken by laurie be (y-d)/2x + t? Where d is the remaining distance laurie has to walk.

I followed the same logic, yet the official answer is listed as C.

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