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Homework Help: Comparison Problem

  1. May 8, 2017 #1
    1. The problem statement, all variables and given/known data

    Which is greater?
    2. Relevant equations

    Equation is provided in the question
    3. The attempt at a solution
    let y=1:
    LHS= 1
    So LHS & RHS are equal.

    2ND try;
    LET Y=0
    LHS= 0.4
    RHS= 0
    So LHS is greater.
    So Answer cant be determined using the information provided.

    However my answer not correct. Some body please guide me.

  2. jcsd
  3. May 8, 2017 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Do you know how to find the values of y where they are equal? If so, you can just test once in each of the other sections and see how they compare.
  4. May 8, 2017 #3
    ##f(y) := (3y+2)/5 - y = (3y + 2 - 5y)/5 = (2 - 2y)/5##

    ##f(y) > 0## for ##y < 1## and negative elsewhere. So I think you are correct.

    Maybe the domain is mentioned. did you wrote exact question ?
  5. May 9, 2017 #4
    Thanks. You are right. I skipped the assumption:
    y>4. Now if y=5 then:
    LHS= 17/3= 3.666
    RHS=5 so RHS is greater.

    Let y=20
    LHS= 62/5= 12.4
    RHS= 20

    so again RHS is greater.

    So RHS is greater.

    Thanks for your comment.

  6. May 9, 2017 #5


    Staff: Mentor

    Assuming, as you later wrote, that y > 4, solve the inequality (3y + 2)/5 > y. This is equivalent to y < 1.
    This means that if y < 1, the left side will be larger than the right side.

    Put another way, if y < 1, the right side will be smaller than the left side. If y > 1, the right side will be larger. Your two examples, with y = 5 and y = 20 both support this conclusion.
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