Results 1 to 3 of 3

Math Help - Equation help

  1. #1
    Newbie
    Joined
    Nov 2008
    Posts
    2

    Unhappy Equation help

    The teacher gave this problem. She gave the weight of an old penny as 3.09g and the weight of a new penny as 2.51g. There are ten pennies in a container and the combined weight is 26.78. She wants an equation to find how many of each penny is in the container. The equation created was 3.09X+2.51y=26.78. Was told that this is incorrect because cannot have two variables in this equation.
    Help. Mom lost.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    You're on the right track, you just need a 2nd equation because you do have two variables to solve for. The total amount of pennies is 10, so you can also say x+y=10.

    3.09x+2.51y=26.78
    x+y=10

    Now you either use y=10-x or x=10-y to make a substitution into the 1st equation and solve for them both.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2008
    Posts
    2
    We were substituting the wrong set of numbers. There was a second container with pennies as well and I was trying to solve for x and substitute that set but it wasn't working. I guess it's been too long since I did algebra. Thanks so much for putting us on the right track.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: April 11th 2011, 01:17 AM
  2. Partial differential equation-wave equation - dimensional analysis
    Posted in the Differential Equations Forum
    Replies: 3
    Last Post: August 28th 2009, 11:39 AM
  3. Replies: 2
    Last Post: May 18th 2009, 12:51 PM
  4. Replies: 2
    Last Post: April 28th 2009, 06:42 AM
  5. Replies: 1
    Last Post: October 23rd 2008, 03:39 AM

Search Tags


/mathhelpforum @mathhelpforum