1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Continuous random variable={-b-(b^2-4ac)^.5}/(2a)=x?

  1. Apr 19, 2007 #1

    inv

    User Avatar

    [Solved]Continuous random variable={-b-(b^2-4ac)^.5}/(2a)=x?

    1. The problem statement, all variables and given/known data
    A factory is supplied with grain at the beginning of ea week.The weekly demand,X thousand tonnes for grain from this factory is a continuous random variable having the probability density function given by
    f(x)=2(1-x),0<x<1
    0 ,otherwise
    Find the quantity of grain in tonnes the factory should've in stock in the beginning of a week in order to be 98% certain that the demand in that week will be met.

    *I've found 2 answers but the answer sheet only chose 1 of 'em,found by using the (-b-(b^2-4ac)^.5)/(2a)


    2. Relevant equations
    (-b+(b^2-4ac)^.5)/(2a)


    3. The attempt at a solution

    I've integrated f(x) with the lower x value and higher x value 0 and 1 respectively and got:
    [2x-x^2]=0.98
    0=x^2-2x+0.98
    (-b+(b^2-4ac)^.5)/(2a)
    x=1.14 and 0.859
    *I don't know why the answer sheet chose only the 0.859,why?
     
    Last edited: Apr 19, 2007
  2. jcsd
  3. Apr 19, 2007 #2

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    What's the domain of f in the orginal question?
     
  4. Apr 19, 2007 #3

    inv

    User Avatar

    Domain of f is x,domain is x and range is y.That's what u want?
     
  5. Apr 19, 2007 #4

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    No, sorry, I'll rephrase my question. The function f is only defined for certain values of x. What are these? Are both of your answers in the interval of allowed x values?
     
  6. Apr 19, 2007 #5

    inv

    User Avatar

    No_Only 1 of 'em're,which makes this case solved.Tq so much for making me realize.
     
  7. Apr 19, 2007 #6

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    No, the domain of a function is the set of possible values for x- and those are given in the problem.
     
  8. Apr 19, 2007 #7

    inv

    User Avatar

    Thanks for the reply a bunch Ivy ,bye.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Continuous random variable={-b-(b^2-4ac)^.5}/(2a)=x?
Loading...