Results 1 to 5 of 5

Math Help - last thread for the night

  1. #1
    Newbie
    Joined
    Jun 2006
    Posts
    11

    last thread for the night

    lastthread for the night, thanks if you can help me with these last problems




    In the formula A=lw, If l is constant, A varies___________ as w



    A large concrecte mixing machine can mix a certain ammount of concrete in 12 hours, while a smaller one can mix the same ammount in 20 hours, Mixing simultaneously, how long would it take both machines to mix the same ammount of concrete?




    For a school play, students tickets cost 40cent and adult tickets were 75 cen t. The total receipts for 90 tickets were $46.50. How many of each kind were sold?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    Quote Originally Posted by Aarxn
    In the formula A=lw, If l is constant, A varies___________ as w
    It is "directly".

    There are two proportions. Direct and Inverse.
    Inverse is when two variables mutiply to a constant, thus,
    xy=k thus, y=\frac{k}{x}- they form a hyperbola.

    Direct proprtion is when two variables divide to give a constant, thus,
    \frac{y}{x}=k thus, y=kx-they form a line.

    The case here is,
    A=lw where "l" is a constant, thus we have a direct proportion.

    To learn more about direct and inverse proprtions.
    Do not under any condition press on this link.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    Quote Originally Posted by Aarxn
    A large concrecte mixing machine can mix a certain ammount of concrete in 12 hours, while a smaller one can mix the same ammount in 20 hours, Mixing simultaneously, how long would it take both machines to mix the same ammount of concrete?
    I have a useful formula for such problem.
    If it takes something a units of time to do a job and it takes b units of times the same job. Then working together would take:
    \frac{ab}{a+b}
    In this case, a=12,b=20 thus together it takes,
    \frac{12\cdot 20}{12+20}=7.5\mbox{ hours}
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    Quote Originally Posted by Aarxn
    For a school play, students tickets cost 40cent and adult tickets were 75 cen t. The total receipts for 90 tickets were $46.50. How many of each kind were sold?
    Let, x be # of adults
    Let, y be # ot students.

    Thus,
    x+y=90
    In total the students paid, .4x
    while the adults paid, .75y
    The net price was therefore, .4x+.75y
    but the example says that was 46.50 thus,

    \left\{ \begin{array}{c} x+y=90\\.4x+.75y=46.5
    In the first equation solve for "y" thus,
    y=90-x and substitute that into equation 2,
    .4x+.75(90-x)=46.5
    Open parantheses,
    .4x+67.5-.75x=46.5
    Subtract "67.5" from both sides and combine x terms,
    -.35x=-21
    divide both sides by (-.35) thus,
    x=60 thus, y=30
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jun 2006
    Posts
    11
    thank you once again for helping me
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. One last question for the night...
    Posted in the Advanced Algebra Forum
    Replies: 4
    Last Post: October 28th 2010, 08:13 PM
  2. last question of the night..thank goodness
    Posted in the Calculus Forum
    Replies: 1
    Last Post: December 17th 2009, 12:45 AM
  3. Help me on these all night stumpers
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: August 28th 2009, 02:34 PM
  4. having a slow night!
    Posted in the Algebra Forum
    Replies: 3
    Last Post: August 7th 2009, 01:54 PM
  5. Two More Questions For The Night.
    Posted in the Algebra Forum
    Replies: 4
    Last Post: March 12th 2009, 12:44 AM

Search Tags


/mathhelpforum @mathhelpforum