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NMAT Tricky Math Problem: 3^(n+2)+(3^(n+3)-3^(n+1)) = ?

  1. Nov 30, 2012 #1
    1. The problem statement, all variables and given/known data
    The problem is from an NMAT Practice Exam. The problem is multiple choice.

    3^(n+2)+(3^(n+3)-3^(n+1)) = ?

    a.)1/(3^(n+1))
    b.)1/(3^(n+2))
    c.)3/8
    d.)1/3

    The answer given is 1/3, but I don't know how they got that.

    2. Relevant equations
    none


    3. The attempt at a solution

    My attempts:
    3^(n+2)+(3^(n+3)-3^(n+1)) =3^(n)*(9+27-3)=33*3^n

    Another attempt using self similarity...

    y=3^(n+2)+(3^(n+3)-3^(n+1))
    3y=3^(n+3)+(3^(n+4)-3^(n+2))
    3y-y=3^(n+4)-2*3^(n+2)+3^(n+1)
     
  2. jcsd
  3. Nov 30, 2012 #2

    symbolipoint

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    None of the choices is correct. My result is 11*3^(n+1)

    Did you type the expression exactly as given to you?
     
  4. Nov 30, 2012 #3
    Thanks for the reply. Yes I typed it correctly. That's the same answer I got, but it's none of the choices. It's a practice exam for entrance into Medical School (I'm helping someone out with the math part) so I thought I was overlooking something, but I guess the practice problem is just wrong. However, it is under the inductive reasoning section of the practice exam so I thought it was trick question. Thanks again.
     
  5. Nov 30, 2012 #4
    I asked it on Math Stack Exchange and they figured out that + is probably a test typo and suppose to be a divide symbol, which gives an answer of 3/8. Sorry for the trouble. Thanks.
     
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