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Math Help - Algebra riddle

  1. #1
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    Algebra riddle

    A woman buys "x" cakes at 45p each and (x+8) cakes at 55p each. \If she wishes to have change from a 20 note work out what "x" is?

    I have come up with :

    0.45x+0.55(x+8)=<20

    Am I on the right track?

    And...

    A boy buys some packets of sweets for 1.20. If the sweets had been 3p a pack cheaper he would have recieved 2 more packets for his money. How many packets did he buy?

    I got 78 for my answer, is this correct?

    Thanks in advance

    381
    Last edited by mr fantastic; January 28th 2009 at 11:12 AM. Reason: Deleted question restored
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  2. #2
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    0.45x+0.55(x+8)=<20
    very close. Since she wishes to have change, it should be 0.45x+0.55(x+8)<20

    A boy buys some packets of sweets for 1.20. If the sweets had been 3p a pack cheaper he would have recieved 2 more packets for his money. How many packets did he buy?

    I got 78 for my answer, is this correct?
    No. Let c be the price and p be the number of packets he originally bought.
    We know that pc=120 and (p+2)(c-3) = 120. So we have 2 equations with 2 unknowns and can solve simultaneously.
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  3. #3
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    For the cake question: I have the formula constructed properly, but what do i do with it now

    for the sweet question: And as for the simultaneous equations i have ended up with -3p+2c=6
    im sure i have gone wrong somewhere along the line, could you take me through the steps for soving this one please

    thanks in advance

    381
    Last edited by mr fantastic; January 28th 2009 at 11:13 AM. Reason: Deleted question restored
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  4. #4
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    still need help on this if anyone can help?

    A woman buys "x" cakes at 45p each and (x+8) cakes at 55p each. \If she wishes to have change from a 20 note work out what "x" is?

    I have come up with :

    0.45x+0.55(x+8)=<20

    0.45x+0.55x+4.4=<20

    0.45x+0.55x=15.6

    x=15.6

    Am I on the right track?
    Last edited by mr fantastic; January 28th 2009 at 11:14 AM. Reason: Deleted question restored
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  5. #5
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    Riddle

    Hello tomh381
    Quote Originally Posted by tomh381 View Post
    still need help on this if anyone can help?

    A woman buys "x" cakes at 45p each and (x+8) cakes at 55p each. \If she wishes to have change from a 20 note work out what "x" is?

    I have come up with :

    0.45x+0.55(x+8)=<20

    0.45x+0.55x+4.4=<20

    0.45x+0.55x=15.6

    x=15.6

    Am I on the right track?
    Your algebra is fine, except that, as badgerigar has pointed out, you should have x < 15.6.

    The question now is: what do you do with this answer? Well, x must be a whole number, mustn't it? So if the question is asking you for the greatest value of x (and you haven't actually said that it is), then you obviously want the largest whole number that is less than 15.6. That's not very hard, is it?

    Grandad

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  6. #6
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    Lol, Thanks for all your help and, yes, I had realised to round down to nearest whole number, whose ever heard of 15.6 cakes!?!?!? lol

    so x=15 ...HAPPY DAYS...

    Thanks again folks, a great resource here
    Last edited by mr fantastic; January 28th 2009 at 11:15 AM. Reason: Deleted question restored
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