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Math Problem [ Help ]

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Fleur775 -  
Hello, I can't solve this damn math problem!! Grrr.
Please help me :(

Kévin and Zoé choose the same number together and "type" on their calculator,

(number)x8-15=(result)

while Zoé presses the keys:

(number)-1=(number)x4+6=(result)

Kévin and Zoé notice that they both get the same result.
What number did Kévin and Zoé choose in the first place?

Thank you in advance.. :$

5 answers

  1. Anonymous user
    You got it right

    Okay, let's go again.

    8x - 15 = y
    x - 1 = y => we isolate x: x = y + 1

    This gives

    8 ( y + 1 ) - 15 = y by replacing in the first equation x with y + 1

    You expand:

    8 y + 8 - 15 = y
    7 y = 7
    y = 1

    You replace y in the second equation x = y + 1
    x = 1 + 1 = 2

    So the number chosen at the beginning is x = 2 and the result they find is y = 1
    --
    Best regards,

    Mezzzman
    8
    1. Anonymous user
      Hi,

      You need to solve the system of two equations:

      1) 8x - 15 = y
      2) x - 1 = y

      You express x as a function of y in equation 2)

      This gives you:

      x = y + 1

      And you replace x with y + 1 in 1)

      Let me know what you find, and I'll validate it afterwards! :)
      --
      Best regards,

      Mezzzman
      5
      1. Fleur775 Author
        Oh my god, I'm lost :'(

        So basically: 8y + 1 - 15 ??

        Sorry .. But could you try to break it down for me, please, because math is my enemy.
        3
        1. Teenager42
          8x - 15 = y
          x - 1 = y

          8x-15=x-1

          8x-15+1=x

          -15+1=x-8x

          -14=x(1-8)

          -14/-7=x

          x=2

          but it doesn't work with (number)x4+6
          1
          2. Fleur775 Author
            Oh I see! :PPP THANK YOU SO MUCH!! :)
            2