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Homework Help: Simultaneous equation help

  1. Mar 30, 2008 #1
    1. The problem statement, all variables and given/known data
    A zookeeper spends $133.10 altogether on bananas and nuts for the monkeys.
    He buys 8 kilograms more bananas than nuts.
    Bananas cost $2.20 per kilogram and nuts cost $4.80 per kilogram.
    How many kilograms of bananas did the zookeeper buy?
    You must show the equations that you use to solve the problem.

    3. The attempt at a solution

    I think this has somthing to do with simultaneous equations but i don't know how to make them out of the question...
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 30, 2008 #2
    This is one of those problems that you need to read several times and write down the things that you know:
    You know there are bananas (B) and nuts(N)
    so the total is.......?
    Then there are 8kg more B than N
    so B+?=N.....
    see if you can come up with a system from that.
    You will be finding the total kg and dividing by the prices given.
  4. Mar 30, 2008 #3
    so would the first simutaneous equation be:

  5. Mar 30, 2008 #4
  6. Mar 30, 2008 #5
    I don't see what the second one would be though... at a guess i would say it would be:

  7. Mar 30, 2008 #6
    Are there more Bananas or nuts? for the second one?
    I had to reread the question. Sorry for the edit.

  8. Mar 30, 2008 #7
    What do you mean by the same form?
  9. Mar 30, 2008 #8
    Well, for the first equation, you have
    then for the second one (check my first post) you will have:
    so you have B and N on the same side in the first equation, so you need the second equation to look like the first one in terms of where the B and N are. (also known in the nerdy math world as "standard form".)
  10. Mar 30, 2008 #9
    So would that be B+N=133.10 and then you sub N=B+8 for the value of N so it looks like:


    i'm not sure...
  11. Mar 30, 2008 #10
    You're right. You got it.
    Now you need to get your second equation to look like the first one...you need all letters on one side and the numbers on the other. Then you stack them on top of each other and there's your system.
  12. Mar 30, 2008 #11
    is the next step b^2=125.10?
  13. Mar 30, 2008 #12
    You got:
    B+(B+8)..not so much....

    look, if N=B+8,(which is right)
    and you want the N and B on the same side of the "=" sign, what do you need to do?
    Forget the B+(B+8)..you are making this harder than it is meant to be.
  14. Mar 30, 2008 #13
    If the equation is B+8=N then you take N from both sides and take 8 from both sides so it would be B-N=-8

    Is that right?
  15. Mar 30, 2008 #14
  16. Mar 30, 2008 #15
    then do I go 2B=125.10

    then B=62.55?
  17. Mar 30, 2008 #16
    yes yes
    then to figure the kg, what?
  18. Mar 30, 2008 #17
    divide by 2.20?
  19. Mar 30, 2008 #18
    you got it!
  20. Mar 30, 2008 #19
    Now you have to do the Nuts!
  21. Mar 30, 2008 #20
    so the amount of bananas in kgs is 62.55/2.20=28.43 kgs (2dp)?

    And the amount of nuts is 28.43/8=3.55 kgs?
  22. Mar 30, 2008 #21
    you lost ME there.
    What did you get for the N when you solved for it?
    Why divide by 8?
    I got 28.43 for Bananas......
  23. Mar 30, 2008 #22
    I got 3.55 kgs for nuts as the question says there is 8 times as many bananas than nuts.... Is that not right?
  24. Mar 30, 2008 #23
    As the question is stated, the zookeeper buys 8 MORE kg, not 8 TIMES more
    Go back to your original equations and plug in there
  25. Mar 30, 2008 #24
    so its 20.43 kgs of nuts?
  26. Mar 30, 2008 #25
    you had:
    you solved for B and you got
    HOW can you get N from that?
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