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Homework Help: Integration problem

  1. Mar 20, 2010 #1
    1. The problem statement, all variables and given/known datathe lifetime of a machine part has a continuous distribution on the interval(0,40) with probability density function f, where f(x) is proportional to (10 + x)^(-2) Calculate the probability that the lifetime of the machine part is less than 6.

    2. Relevant equations

    3. The attempt at a solutionMy book says that since f(x) is proportional to (10 + x), f(x)=k(10+x)^(-2). My question is why we need to put the k in the equation? Is it merely because the question says that they're proportional and so we need to set up that integration to find by how much they're proportional?
  2. jcsd
  3. Mar 20, 2010 #2


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