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Distance from average speed

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Striver Just gettin' started! Default Avatar
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Distance from average speed Post Fri Jun 08, 2012 7:30 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    If it took Carlos ½ hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile = 5,280 feet)

    (1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.

    (2) The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second.

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    Post Fri Jun 08, 2012 8:53 am
    Striver wrote:
    If it took Carlos ½ hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile = 5,280 feet)

    (1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.

    (2) The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second.
    Since the two statements are in terms of FEET PER SECOND, rephrase the question stem in terms of FEET PER SECOND.

    1/2 hour = 1800 seconds.
    Determine the rate needed to travel 6 miles in 1800 seconds:
    (6 miles)/(1800 seconds) * (5280 feet)/(1 mile) = (6*5280)/1800 = 528/30 = 176/10
    = 17.6 feet per second.

    Thus, to travel MORE than 6 miles in 1800 seconds, the average speed must be GREATER than 17.6 feet per second.
    Question rephrased:
    Was the average speed greater than 17.6 feet per second?

    The two statements combined indicate only that the average speed was between 16 feet per second and 18 feet per second, implying that the average speed could be less than, equal to, or greater than 17.6 feet per second.
    INSUFFICIENT.

    The correct answer is E.

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    khandelwal.ab Just gettin' started! Default Avatar
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    Post Fri Jun 08, 2012 9:29 am
    I spent about three minutes to get to the answer here. However if I had rephrased the stem as Mitch did, I would have spent less then a minute.

    A perfect question that made me realise that you should ALWAYS rephrase the stem.

    gmattesttaker2 Really wants to Beat The GMAT! Default Avatar
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    Post Sun Jun 10, 2012 11:46 pm
    Hello Mitch,

    Had a question. I was wondering why we are calculating the rate here.

    Will the following be correct here: Speed = Distance/Time. I was trying this approach:

    16 ft. = Distance/1800 sec

    and once I found Distance I wanted to compare whether it was greater than 6 miles.

    Sorry I am not too good with some of these problems. Thanks a lot for your help.

    Regards,
    Sri

    dhonu121 GMAT Destroyer! Default Avatar
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    Post Mon Jun 11, 2012 2:11 am
    Striver wrote:
    If it took Carlos ½ hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile = 5,280 feet)

    (1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.

    (2) The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second.
    Distance = speed*time.
    Distance = speed*.5 hours.
    Thus s/2=d>6
    or s>12 miles/hour is the question in simplified form.
    from 1:s>16ft/sec.
    Convert it to miles/hour.
    16*(1/5280miles)/(1/3600hours)
    16*(3600/5280) = 10.9 Miles/hour.
    Insufficient.

    From 2:
    s<18ft/sec
    converting to miles/hour = 18*(3600/5280)=12.27
    Insufficient.

    Combining 1 and 2 we get that
    10.9<s<12.27.
    Insuff.
    hence correct answer is E.

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    Post Tue Jun 12, 2012 7:53 pm
    Hello Dhonu,

    Hope all is well. Thank you very much for your kind reply and for your thorough explanation. Now it is clear. Thanks again.

    Best Regards,
    Sri

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