Results 1 to 3 of 3

Math Help - Worded max/min problem

  1. #1
    Junior Member
    Joined
    Feb 2009
    Posts
    59

    Worded max/min problem

    A piece of wire 20cm long is cut into two pieces. One piece is used for a square shape and the other a circle shape with radius r cm.

    i) write down the area and the perimeter of the circle in terms of r.
    I would go
    A = ∏r^2
    A/r^2 =
    r^2 = A/
    r = sqrt(A/∏)

    P = 2∏r
    r = P/2
    But not sure if this is right

    ii) find the perimeter of the square in terms of r
    iii) using your answer in part ii) state the length of one side of the square in terms of r.
    iv) find the area of the square in terms of r
    v) find the total area A cm^2 of the circle and the square in terms of r
    i'm unsure how to do these one any help would be greatly appreciated!!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Grandad's Avatar
    Joined
    Dec 2008
    From
    South Coast of England
    Posts
    2,570
    Thanks
    1

    Word problem

    Hello scubasteve94
    Quote Originally Posted by scubasteve94 View Post
    A piece of wire 20cm long is cut into two pieces. One piece is used for a square shape and the other a circle shape with radius r cm.

    i) write down the area and the perimeter of the circle in terms of r.
    I would go
    A = ∏r^2
    A/r^2 =
    r^2 = A/
    r = sqrt(A/∏)

    P = 2∏r
    r = P/2
    But not sure if this is right

    ii) find the perimeter of the square in terms of r
    iii) using your answer in part ii) state the length of one side of the square in terms of r.
    iv) find the area of the square in terms of r
    v) find the total area A cm^2 of the circle and the square in terms of r
    i'm unsure how to do these one any help would be greatly appreciated!!
    In part (i), you have the right formulae for A and P, but you don't need to change them around to make r the subject. Just leave them as:

    A = \pi r^2 and P = 2\pi r

    (ii) The key fact you have to use for the next bit is that if you have used P cm to make the circle ( = 2\pi r) then you'll have (20-P) cm of wire left to make the square. So that's the perimeter of the square. But we want it in terms of r, so we simply say: the perimeter of the square is (20 - 2\pi r) cm.

    (iii) How do you find the length of one side of a square if you know its perimeter? Well just do that to (20 - 2\pi r) and there's the answer. (Note: in algebra, when you're dividing by something, it's often easiest to write the result as a fraction. So a \div b, for instance, is usually written \frac{a}{b}.}

    (iv) Square your answer to part (iii).

    (v) Add together your area answers to (i) and (iv).

    Can you complete it now?

    Grandad
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by scubasteve94 View Post
    A piece of wire 20cm long is cut into two pieces. One piece is used for a square shape and the other a circle shape with radius r cm.

    i) write down the area and the perimeter of the circle in terms of r.
    I would go
    A = ∏r^2
    A/r^2 =
    r^2 = A/
    r = sqrt(A/∏)

    P = 2∏r
    r = P/2
    But not sure if this is right

    ii) find the perimeter of the square in terms of r
    iii) using your answer in part ii) state the length of one side of the square in terms of r.
    iv) find the area of the square in terms of r
    v) find the total area A cm^2 of the circle and the square in terms of r
    i'm unsure how to do these one any help would be greatly appreciated!!
    Read this thread: http://www.mathhelpforum.com/math-he...perimeter.html
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Worded Problem
    Posted in the Algebra Forum
    Replies: 3
    Last Post: December 6th 2011, 02:39 PM
  2. Worded problem.
    Posted in the Algebra Forum
    Replies: 6
    Last Post: January 2nd 2011, 05:44 PM
  3. Worded problem.
    Posted in the Algebra Forum
    Replies: 2
    Last Post: August 20th 2010, 07:41 PM
  4. worded log problem
    Posted in the Algebra Forum
    Replies: 3
    Last Post: July 2nd 2008, 01:33 PM
  5. Worded problem.
    Posted in the Business Math Forum
    Replies: 0
    Last Post: March 18th 2008, 05:56 AM

Search Tags


/mathhelpforum @mathhelpforum