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Math Problem [ Help ]

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Fleur775 Posted messages 48 Status Member -  
Fleur775 Posted messages 48 Status Member -
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
  2. 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
  3. Fleur775 Posted messages 48 Status Member 9
     
    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
  4. Fleur775 Posted messages 48 Status Member 9
     
    Oh I see! :PPP THANK YOU SO MUCH!! :)
    2
  6. Teenager42 Posted messages 94 Registration date   Status Member Last intervention   11
     
    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