Results 1 to 4 of 4

Math Help - Help on problems.

  1. #1
    Ash
    Ash is offline
    Junior Member
    Joined
    Nov 2006
    Posts
    56

    Help on problems.

    I'm not sure about solving problems, #1 and #2.
    There seems to be different ways to answering these types of problems and the information/question they give varies form problem to problem. Is there a universal setup for these types of problems?


    #1
    A biologist wishes to have 15 gallons of an 80% formaldehyde solution. In her inventory, she has pure formaldehyde and some 50% formaldehyde solution. How many gallons of each should she mix to obtain the desired solution?


    So do I set up the equation 2x+.50(15-x)=15(.80)
    so x=3 gallons? ,15-3= 12 gallons

    #2
    A leather finisher determines that his 8-ounce solution of 12% boric acid is too weak. How many ounces of pure boric acid must be added to increase the concentration to 20%

    15*(.12)which would equal: .96+x. Does that express what is needed to increase the boric acid and where does the 20% come in to play?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Ash View Post
    I'm not sure about solving problems, #1 and #2.
    There seems to be different ways to answering these types of problems and the information/question they give varies form problem to problem. Is there a universal setup for these types of problems?


    #1
    A biologist wishes to have 15 gallons of an 80% formaldehyde solution. In her inventory, she has pure formaldehyde and some 50% formaldehyde solution. How many gallons of each should she mix to obtain the desired solution?


    So do I set up the equation 2x+.50(15-x)=15(.80)
    so x=3 gallons? ,15-3= 12 gallons
    I think you will find it easier to follow what is going on if you include more
    text saying what you are doing.

    Let x be the number of gallons of 100% solution, and y be the number of
    gallons of 50% solution of formaldehyde used. Then as there are 15 gallons
    altogether:

    x + y =15.

    Also the 15 gallons contains 0.8*15 gallons of pure formaldehyde, while
    x gallons of the 100% solutions contain x gallons or pure formaldehyde, and
    y gallons of 50% solution contain 0.5*y or pure formaldehyde, so:

    0.8*15 = x + 0.5*y,

    or rearranging:

    x + 0.5 y = 12

    so now we have two equations:

    x + y = 15
    x + 0.5y =12

    which we solve to find that y=6 gallons and x = 9 gallons.

    RonL
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by Ash View Post
    #2
    A leather finisher determines that his 8-ounce solution of 12% boric acid is too weak. How many ounces of pure boric acid must be added to increase the concentration to 20%

    15*(.12)which would equal: .96+x. Does that express what is needed to increase the boric acid and where does the 20% come in to play?
    Let the number of onces of pure boric acid added be x, then we have 8+x
    ounces of solution, which contains 0.12*8 + x ounces of pure boric acid.

    So as the final concentration is 20%:

    (0.12*8 + x)/(8 + x) = 0.2

    or:

    0.96 + x = 1.6 + 0.2 x

    so:

    0.8 x = 1.6 - 0.96,

    so: x = 1.05 ounces.

    RonL
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Ash
    Ash is offline
    Junior Member
    Joined
    Nov 2006
    Posts
    56
    Quote Originally Posted by CaptainBlack View Post
    I think you will find it easier to follow what is going on if you include more
    text saying what you are doing.


    RonL


    Thanks for your help! Next time I will include more text so that the part I am not doing right or understanding can be easier identified.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: October 3rd 2011, 05:35 AM
  2. binomial problems/normal problems
    Posted in the Statistics Forum
    Replies: 1
    Last Post: October 19th 2010, 11:46 PM
  3. binomial problems as normal problems
    Posted in the Statistics Forum
    Replies: 1
    Last Post: October 19th 2010, 11:41 PM
  4. Problems with integration word problems
    Posted in the Calculus Forum
    Replies: 5
    Last Post: April 25th 2010, 05:39 PM
  5. 2 Problems, need help, story problems!
    Posted in the Algebra Forum
    Replies: 3
    Last Post: October 23rd 2007, 10:43 PM

Search Tags


/mathhelpforum @mathhelpforum