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the number line shown contains 3 points

This topic has 3 expert replies and 3 member replies
peter456 Junior | Next Rank: 30 Posts Default Avatar
Joined
20 Sep 2015
Posted:
24 messages

the number line shown contains 3 points

Post Thu Mar 03, 2016 8:28 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    The number line shown contains 3 points R, S, and T, whose coordinates have absolute values r, s, and t, respectively. Which of the following equals the average of the coordinates of the points R, S, and T?
    (A)s
    (B)s + t + r
    (C)(r-s-t)/3
    (D)(r+s+t)/3
    (E)(s+t-r)/3
    Sorry I can't draw but just an idea;
    <----R------0----S----T---->
    Since the coordinates are given in absolute values, I felt their average
    is simply (r+s+t)/3



    Last edited by peter456 on Sun Mar 06, 2016 6:31 pm; edited 1 time in total

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    Post Thu Mar 03, 2016 9:47 am
    Hi peter456,

    This question can be solved by TESTing VALUES.

    Based on their positions on the number line, we know that S and T are POSITIVE and R is NEGATIVE, so let's TEST...

    R = -3
    S = 1
    T = 2

    Since r, s and t are the ABSOLUTE VALUES of those 3 numbers, we have...

    r = 3
    s = 1
    t = 2

    The question asks for the AVERAGE of R, S and T, so we're looking for an answer that equals (-3 + 1 + 2)/3 = 0/3 = 0.

    (A) s = 3 NOT a match
    (B) s + t + r = 6 NOT a match
    (C) (r-s-t)/3 = 0 This IS a match
    (D) (r+s+t)/3 = 2 NOT a match
    (E) (r+s-t)/3 = 2/3 NOT a match

    Final Answer: C

    GMAT assassins aren't born, they're made,
    Rich

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    peter456 Junior | Next Rank: 30 Posts Default Avatar
    Joined
    20 Sep 2015
    Posted:
    24 messages
    Post Sun Mar 06, 2016 6:24 pm
    Rich.C@EMPOWERgmat.com wrote:
    Hi peter456,

    This question can be solved by TESTing VALUES.

    Based on their positions on the number line, we know that S and T are POSITIVE and R is NEGATIVE, so let's TEST...

    R = -3
    S = 1
    T = 2

    Since r, s and t are the ABSOLUTE VALUES of those 3 numbers, we have...

    r = 3
    s = 1
    t = 2

    The question asks for the AVERAGE of R, S and T, so we're looking for an answer that equals (-3 + 1 + 2)/3 = 0/3 = 0.

    (A) s = 3 NOT a match
    (B) s + t + r = 6 NOT a match
    (C) (r-s-t)/3 = 0 This IS a match
    (D) (r+s+t)/3 = 2 NOT a match
    (E) (r+s-t)/3 = 2/3 NOT a match

    Final Answer: C

    GMAT assassins aren't born, they're made,
    Rich
    Hi EmpowerGmat,
    The OA is not C; hwever, option E should be (s+t-r)/3, the OA.

    Could u please revisit this question?

    Marty Murray Legendary Member
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    Post Sun Mar 06, 2016 8:57 pm
    peter456 wrote:
    The number line shown contains 3 points R, S, and T, whose coordinates have absolute values r, s, and t, respectively. Which of the following equals the average of the coordinates of the points R, S, and T?
    (A)s
    (B)s + t + r
    (C)(r-s-t)/3
    (D)(r+s+t)/3
    (E)(s+t-r)/3
    Sorry I can't draw but just an idea;
    <----R------0----S----T---->
    Since the coordinates are given in absolute values, I felt their average
    is simply (r+s+t)/3
    We need to find the average of the coordinates. Average = Sum/Number

    The absolute value of a number is the POSITIVE DISTANCE between that number and zero.

    S and T are to the right of 0 on the number line. So the values of their coordinates are greater than 0. So the values of s and t, which are ABSOLUTE values of the coordinates, are the same as the values of the coordinates.

    R is to the left of 0 on the number line. So the value of R's coordinate is less than 0. r is an absolute value. So the value of R's coordinate, which is a negative number, is -r.

    To find the average of the values of the three coordinates, find the sum of the coordinates and divide by the number of coordinates.

    (s + t - r)/3 = the average of the coordinates

    The correct answer is E.

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    Post Sun Mar 06, 2016 11:10 pm
    Hi peter456,

    Since you've made an edit to the original question, I'm curious if you fixed any typos in the answer choices (the original Answer E that I copied from your post doesn't match the current Answer E that is listed there). Regardless, with the "new" Answer E, and the 3 numbers that I chose to TEST, we would have TWO answers that match: BOTH Answer C and Answer E.

    In a situation in which more than one answer appears correct, you have to TEST a "new" set of VALUES, although you don't necessarily have to change all of them. In this case, you can change just the value of R and r and you'll get the correct answer.

    If we TEST:

    R = -4
    S = 1
    T = 2

    Then we have....

    r = 4
    s = 1
    t = 2

    The average of R, S and T equals -1/3, so we're looking for THAT result in Answers C and E.

    (C)(r-s-t)/3 = +1/3 NOT a match

    (E)(s+t-r)/3 = -1/3 This IS a match

    Final Answer: E

    GMAT assassins aren't born, they're made,
    Rich

    _________________
    Contact Rich at Rich.C@empowergmat.com

    peter456 Junior | Next Rank: 30 Posts Default Avatar
    Joined
    20 Sep 2015
    Posted:
    24 messages
    Post Fri Mar 11, 2016 9:20 am
    My line of reasoning is that since r, s, and t are non-zero positive values, their average should be
    (r+ s + t)/ 3...given that |R| = r; |S|=s; |T|=t

    Kindly point where am making errors

    Thank you

    Post Fri Mar 11, 2016 9:34 am
    Hi peter456,

    The prompt asks for the average of R, S and T. From the number line, we can see that R is NEGATIVE though, so that is going to impact the sum of those three variables.

    The variables r, s and t are all POSITIVE, since they're the respective absolute values of R, S and T. If you were taking the average of THESE 3 variables, the result would ALWAYS be positive. When taking the average of R, S and T though, the average could end up negative or 0. Thus, Answer D cannot be correct.

    GMAT assassins aren't born, they're made,
    Rich

    _________________
    Contact Rich at Rich.C@empowergmat.com

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