Results 1 to 2 of 2

Math Help - Diect proportion

  1. #1
    Member helloying's Avatar
    Joined
    Jul 2008
    Posts
    177

    Diect proportion

    The price $p of a steel ball is proportional to the cube of its radius x cm It is known that the price is $48 for a teel ball of certain radius R cm. Find the price of a steel ball of radius R/2 cm . Ans is $6.

    Please explain to me how to solve why is it $6
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jun 2008
    Posts
    792
    Given:
    p = kr^3 for some constant k.

    48 = kR^3

    p = k\left(\frac{R}{2}\right)^3


    Now, let's rearrange the third equation:

    p = k\frac{R^3}{8} \implies 8P = kR^3

    Notice tha kR^3 from second equation equals 48, so substitute:

    8p = 48

    p = ...
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Inverse proportion/Direct proportion question
    Posted in the Statistics Forum
    Replies: 3
    Last Post: September 26th 2011, 08:22 AM
  2. Proportion
    Posted in the Geometry Forum
    Replies: 1
    Last Post: December 14th 2010, 04:01 PM
  3. Proportion
    Posted in the Algebra Forum
    Replies: 3
    Last Post: November 4th 2010, 02:13 PM
  4. Replies: 3
    Last Post: July 6th 2009, 08:25 PM
  5. Proportion?
    Posted in the Algebra Forum
    Replies: 1
    Last Post: November 12th 2008, 02:45 PM

Search Tags


/mathhelpforum @mathhelpforum