Results 1 to 3 of 3

Math Help - formula please?

  1. #1
    Newbie
    Joined
    Jan 2011
    Posts
    9

    formula please?

    3 rabbits cost 19.70
    the second rabbitt cost 2 more than the first
    the third rabbitt cost 80p less than the second
    what is the cost of the first rabbitt

    can someone please tell me the formula
    Follow Math Help Forum on Facebook and Google+

  2. #2
    -1
    e^(i*pi)'s Avatar
    Joined
    Feb 2009
    From
    West Midlands, England
    Posts
    3,053
    Thanks
    1
    Let the rabbits be U_1, U_2\ and\ U_3 respectively

    You are told U_1 + U_2 + U_3 = 19.70

    U_2 = U_1 + 2

    U_3 = U_2 - 0.8

    Can you use substitution to find U1? (My answer and working are in the spoiler if you wish to check but remember you're only cheating yourself if you don't bother trying)

    Spoiler:
    U_3 = (U_1+2)-0.8 = U_1 + 1.2 this make sense since 2-80p = 1.20

    Back to our first equation

    U_1 + (U_1+2) + (U_1+1.2) = 19.70

    You can collect like terms and solve easily

    Spoiler:
    3U_1 + 3.2 = 19.7

    3U_1 = 16.50

    U_1 = 5.50




    I get an answer of 5.50 which follows because we'd get

    5.50 + 7.50 + 6.70 = 13+6.70 = 19.70
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    Joined
    Dec 2007
    From
    Ottawa, Canada
    Posts
    3,102
    Thanks
    68
    Once you're comfortable with the 3 variables method, you can do it quicker this way:
    1st = a
    2nd = a + 2
    3rd = a + 2 - .8 = a + 1.2

    (a) + (a+2) + (a+1.2) = 19.7
    3a + 3.2 = 19.7
    3a = 16.5
    a = 5.5
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 4
    Last Post: July 15th 2011, 01:30 PM
  2. Replies: 8
    Last Post: September 5th 2010, 12:11 PM
  3. Replies: 1
    Last Post: April 26th 2010, 07:16 PM
  4. Velocity formula from a position formula
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 5th 2009, 02:50 PM
  5. Replies: 8
    Last Post: March 3rd 2009, 11:14 AM

Search Tags


/mathhelpforum @mathhelpforum