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Help on volume

  1. Mar 7, 2009 #1
    plz help me thank you so much ^^(I need help quick before the due date thanks)

    Here the problem:

    A soup company decides to increase the height of its can by 30% but to maintain their present volume. To the nearest percent, how much must the radius of the can be decreased to hold the volume constant.

    (there a picture of the can which is a plain cyclinder)

    I try working backward for the equation to find the volume of a cyclinder, but i really don't know if I got that right. please help me
  2. jcsd
  3. Mar 7, 2009 #2
    What's the formula for the volume of a cylinder? Let's use h for the original height and r for the original radius of the can, and h* and r* for the new height and radius. The basic set up is

    old volume = new volume

    where h* = 1.3 h. Just plug this into the equation and solve for r*. Your answer will depend on r, of course.

    Then find the percentage change: (r* - r)/r . The r's will cancel out at this step.
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