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-   -   My lecturer fail me the second time! (https://www.askmehelpdesk.com/showthread.php?t=561368)

  • Mar 11, 2011, 07:47 AM
    henrypoo
    my lecturer fail me the second time!
    A ship travels between two ports. The cost of fuel is C=$100(ax+b/x+10)

    Where x is the average speed of the ship in knots (x > 0) and a and b are constants. If the ship travels at 4 knots the cost of fuel is $9000 but at 6 knots it is $7000.

    a) Form two linear equations consist of a and b.
    b) Find the values of a and b.
    c) If there are two ports that are 1000 knots apart, what is the cost of the fuel.
  • Mar 11, 2011, 08:23 AM
    smoothy

    Since you failed it twice already... if someone hands you an answer you are going to fail a third time because you don't understand it.

    How do YOU go about solving it first?

    We HELP you with your homework... we don't DO it for you

    Link to the rules for homework. https://www.askmehelpdesk.com/math-s...-b-u-font.html
  • Mar 11, 2011, 08:24 AM
    Unknown008



    a) Put first C = 9000, x = 4, then a second time using C = 7000 and x = 6.

    You'll get two equations.

    b) Solve those two equations simultaneously.

    c) That questions seems wrong... knots is a measure of speed and two ports cannot be separated by 'some speed'...

    I guess that you have to put x = 1000 and use the values of a and b you got earlier for that.
  • Mar 11, 2011, 08:41 AM
    henrypoo
    If I can understand the question I will not post it in here already.
  • Mar 11, 2011, 09:46 AM
    Unknown008
    Quote:

    Originally Posted by henrypoo View Post
    If i can understand the question i will not post it in here already.

    I agree, but the issue is, you should have posted what you have attempted. This is the usual procedure. Since you were new here, I didn't really impose it, but if you need more help, posting first what you have attempted would be something I'd encourage you to do.

    That said, smoothy was right and his 'thumbs down' was not deserved.

    Okay? :)
  • Mar 11, 2011, 09:49 AM
    smoothy
    Quote:

    Originally Posted by ;
    henrypoo does not find this helpful : at least give some guide

    Firt off. You broke the rules for homework... YOU did take the time to read that link I provided to you Before the rude reddie... didn't you?

    Then you get rude and break another rule about WHEN you are allowed to give a not helpful. Site rules Specifically say you can ONLY do that for inaccurate information. What I gave was completely accurate.

    You never attempted to even try the question... I asked you how you would try to solve it...

    Unknown gave you hints of how to start to solve it... but you want us to hand you the answer without you doing ANY work. Which means you learn nothing and WILL fail it a third time.

    If you can't try... we aren't going to do it for you. That's why you have homework... its to learn how to do something.
    Incidentally... I'm reporting this to site admins.
  • Mar 11, 2011, 09:01 PM
    henrypoo
    But how to solve the equation. Without b how to find a??
  • Mar 12, 2011, 12:02 AM
    Unknown008

    What did you get for part (a) ?
  • Mar 12, 2011, 01:28 AM
    henrypoo
    for part a is 9000=100(ax+b/x+10)

    for part b is 7000=100(a(4)+b/6+10)

    this is where I got stuck. I gt the 2 equation but for the second qns they ask me to find the value of a and b!
  • Mar 12, 2011, 01:50 AM
    henrypoo
    sorry for part a is 9000=100(a(4)+b / 4+10)

    part b is 7000=100(a(6)+b / 6+10)
  • Mar 12, 2011, 02:01 AM
    Unknown008

    Right, can you simplify it a bit? Work out the denominator, then cross multiply for both.

    Note that it's still in part (a). Part (b) is not involved yet.
  • Mar 12, 2011, 10:11 PM
    henrypoo
    9000= (400a+100b / 1400)

    I don't know how to cross multiply cause I never learn this before.
  • Mar 13, 2011, 02:14 AM
    Unknown008

    Part (a)



    Put C = 9000, and x = 4;



    What is 4+10 in the denominator on the right?
    Can you expand the numerator on the right?

    That's the first part in (a)

    Second part in (a), put C = 7000, x = 6



    So the same thing as part one.
  • Mar 13, 2011, 04:01 AM
    henrypoo
    so for part a is it like that?

    9000 = 100(4a+b) / 14
  • Mar 13, 2011, 04:12 AM
    Unknown008

    Yes the first part in part (a) is that. Now multiply both sides by 14, what do you get?
  • Mar 13, 2011, 04:25 AM
    henrypoo
    Multiply both side as in 14 times 9000,100,4a and b?
  • Mar 13, 2011, 04:28 AM
    Unknown008

    No, like this:

    From this:



    to this:



    Can you work this out?
  • Mar 13, 2011, 04:38 AM
    henrypoo
    12,600= 1400(4a+b) / 196 ?
  • Mar 13, 2011, 04:43 AM
    Unknown008

    Not totally true...

    What is 2 times 1/2 ?
  • Mar 13, 2011, 04:46 AM
    henrypoo
    1?

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