GMAT question - Simon and Tim start a race at the same time. Simon c... - Review

Type: Problem Solving

Difficulty: 4 star rating

Simon and Tim start a race at the same time. Simon completes each lap around the racetrack at an average speed of 60mph, and Tim at an average speed of 65mph. How many laps will Simon complete before Tim is a whole lap ahead of him?

  1. 20
  2. 13
  3. 12
  4. 10
  5. 6

Explanation

The speeds of Simon and Tim are in the ratio 60 : 65 which can be simplified to 12 : 13

Therefore Simon will complete 12 laps in the time that Tim completes 13 laps.

So Simon will have completed 12 laps when Tim is a whole lap ahead of him and the correct answer is C.

Comments (5):

  1. I am a little lost where the 10 comes from in the initial equation. I can see that 1/2 is equal to 0.5 miles but the 10? Also, when you divide with fractions doesn't the demoninator flip and you multiple the two together - 1/2 * 1/10.

    Thanks,

    HRC

    Anonymous on 16 Mar 2007 (permalink)

  2. The 10 in the initial equation that you refer to was a mistake and I have replaced it with 5 miles (the relative speed between Simon and Tim).

    Thanks for highlighting this mistake.

    Here's a more detailed version of the division of the fractions involved.

    mathematical expression

    joel on 17 Mar 2007 (permalink)

  3. excuse me, i'm confused when you apply the 1/10 to find out how many miles Simon will travel before Tim laps him, can you please explain again in more detail?

    Thank you

    khodoramer on 28 Sep 2008 (permalink)

  4. This is really quick in the following way...

    Given that the speeds ratio of Simon and Time = 60:65 = 12:13.

    Obviously, if Simon completes 12 laps, Tim will complete 13 laps and hence Tim is 1 lap ahead of Simon. This is all what it is asked in the question.

    So there is no need of the length of the lap to answer this question.

    Sureshbala on 11 Mar 2009 (permalink)

  5. This is a much better explanation than the one originally provided so I have replaced it.

    Thanks.

    joel on 12 Mar 2009 (permalink)

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