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Homework Help: Percentage decrease problem

  1. Jun 22, 2017 #1
    1. The problem statement, all variables and given/known data

    a and B are two variables such that their
    product ab = constant .If a increases by 10%,
    by how much does b decrease ?

    2. Relevant equations

    3. The attempt at a solution

    ab = constant

    If a changes to 11a/10 , then b has to change
    to 10b/11.

    % Change in b is = (b - 10b/11)/b = 9.09%

    b decreases by 9.09% .

    But the answer given is 10% .

    Is 9.09% decrease in b correct ?
  2. jcsd
  3. Jun 22, 2017 #2

    I like Serena

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    Hi Jahnavi,

    Yep, 9.09% decrease in b is correct.
  4. Jun 22, 2017 #3


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    By the same reasoning used to obtain the quoted answer you would get a 100% decrease in b if you increased a by 100%, which is ridiculous.
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