Anonymous
Anonymous asked in Science & MathematicsMathematics · 4 weeks ago

if x-y=15 and 3x+y=13 then y=?

a. -8

b. -7

c. 7

d.8

4 Answers

Relevance
  • 4 weeks ago

    Simulttaneous equations. 

    Add ; this will eliminate 'y' 

    4x = 28 

    x = 7 

    When x = 7 

    7 - y = 15 

    y = 7 - 15 

    y = -8 

    Ans; 'a' 

  • Philip
    Lv 6
    4 weeks ago

    ...x-y = 15...(1).;

    3x+y = 13...(2),;

    [(1)+(2)] ---> 4x = 28, ie., x = 7. Then (1) ---> y = x-15 = -8. a. shows correct answer.

  • 4 weeks ago

     If x - y = 15 and 3x + y = 13 

     then y = -8.

     Answer choice:

     a. -8

  • 4 weeks ago

    You have a system of two equations and two unknowns.  We can solve this with substitution:

    Since you want "y", we'll start with solving the first equation for "x" in terms of "y":

    x - y = 15

    x = 15 + y

    Now substitute this expression in for "x" in the other equation, then solve for y:

    3x + y = 13

    3(15 + y) + y = 13

    45 + 3y + y = 13

    45 + 4y = 13

    4y = -32

    y = -8

    Answer "A".

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