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Thread: Maths problem

  1. #1
    Aug 2012

    Maths problem

    Got given this pdf

    fX(x)=kx(1-x) 0<x>1
    0 otherwise

    Find the constant K? think k=6
    But stuck on the following question:
    Find the range of the Y values and the pdf
    fY(y) of Y when a) Y=-3X+3
    b) Y=1/x
    Can anyone help??
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  2. #2
    MHF Contributor

    Apr 2005

    Re: Maths problem

    I have no idea what you mean by "think k= 6". Why should we think that? If I were asked to find a value of k such that f is a pdf, I would use the fact that the integral 0 to 1 gives the total probability that x is between 0 and 1 which is clealy 1.0. What do you get when you integrate x(1- x) from 0 to 1?

    Your next two questions have missing information. You are essentially asked for the range of the two function, but that depends on the domain, the possible values of x, but I see no domain given here. Normally the "default domain" would be "all values of x for which the function can be calculated" which would be "all real numbers" for (a) and "all real numbers except 0" for (b) but because this is a probability problem, that cannot be true. The integral of each of these functions over the default domain is NOT 1.
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