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Tuesday, August 3, 2010

maths question challenge

mysterious person X has 420 coins, the total value of them equaling $156.
s/he only has 20 and 50 cent coins though!
how many of each coin does s/he have?

this question was in my sisters textbook and it kinda fucked with me a bit. help me out?
at

4 comments:

  1. BrianWednesday, August 4, 2010 at 4:20:00 PM GMT+10

    let x = number of 20c
    let y = number of 50c

    must equal 15600 cents (156 x 100)

    set up simultaneous equations
    x + y = 420 ------> x = 420 - y
    20x + 50y = 15600

    Therefore 20(420 - y) + 50y = 15600
    8400 - 20y + 50y = 15600
    30y = 7200
    y = 240

    Therefore there are 240 50c pieces

    Sub into x + y = 420
    x + 240 = 420
    x = 180

    Therefore there are 180 20c pieces

    CHECK

    180(0.2) + 240(0.5) = $156

    Therefore true

    QED

    Hope i got it right

    ReplyDelete
  2. ȘмžWednesday, August 4, 2010 at 7:50:00 PM GMT+10

    thank you brian!
    the answer was indeed 240 50c and 180 20c coins.

    how easy it was after all...

    but my sisters textbook doesn't do it with simultanious equations, because they haven't learnt that yet. so that's kinda crazy.

    ReplyDelete
  3. BrianWednesday, August 4, 2010 at 8:36:00 PM GMT+10

    you're welcome

    ReplyDelete
  4. Lord of the PalmtreesWednesday, August 4, 2010 at 9:40:00 PM GMT+10

    *IMPLODEs*
    you cool kidz!
    oh and if simultaneous equations dont do it, her textbook probs want some guess and checking to be done. and damn long and worthless process

    ReplyDelete

i say hell no.... u