GMAT question - Mary walked from home to work in the morning at an a... - Review

Type: Problem Solving

Difficulty: 4 star rating

Mary walked from home to work in the morning at an average speed of 3mph. She returned in the evening taking the same route running an average speed of 6mph. What was her average speed for the whole journey to and from work?

  1. 3.5 mph
  2. 4 mph
  3. 4.5 mph
  4. 5 mph
  5. 5.5 mph

Explanation

In this question we are not told, and it does not make any difference, how far Mary has to travel to and from work.

Pick easy numbers

However it will make it easier for us if we assume that it is a nice easy number for our calculations 6 miles say.

Work out the time taken for each part of the trip

Mary walked from home to work in the morning at an average speed of 3mph.

Put this into the appropriate formula for speed, distance and time.

mathematical expression

And

She returned in the evening taking the same route running an average speed of 6mph.

So

mathematical expression

Combine for the total journey

Since we assuming that her journey to work is 6 miles then we can say that her round trip was 12 miles (6 miles to work in the morning and 6 miles back in the evening).

We also know that she takes 3 hours in total (2 hours in the morning and 1 hour in the evening).

mathematical expression

This means that answer B is correct.

Comments (2):

  1. why do we use 6 as our distance or not 3. Do we take the maximum distance. If it is in the data sufficiency question, what do I say with this type of information?

    Amu82 on 23 Oct 2008 (permalink)

  2. The answer will the same whatever distance we use, however, in this case, the math is easiest if we use 6 miles as the distance.

    joel on 30 Oct 2008 (permalink)

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