
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
July 27th, 2018, 12:16 PM  #1 
Newbie Joined: Jan 2018 From: brazil Posts: 4 Thanks: 0  Calculating probabilities
I have a random variable that is defined by this probability function: $\displaystyle f(x) = kx^³$ $\displaystyle 0<x<1$ $\displaystyle f(x) = 0,$ for x outside the above interval It then asks for the probability, so that the variable has a value between 1/4 and 3/4. First I tried to calculate the $\displaystyle \int_{0}^{\infty} f(x)dx = 1 $ to determine the value of k. Then I obtain: $\displaystyle k * \left.\frac{x^4}{4}\right_0^\infty = 1$ This way I will end with: $\displaystyle \infty  0 = 1 $. So what am I doing wrong? Thanks for the time 
July 27th, 2018, 02:05 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,285 Thanks: 1681 
$\displaystyle \int_{0}^{\infty}\!\! f(x)dx = \int_{0}^1\! f(x)dx + \int_{1}^{\infty}\!\! f(x)dx$ and that last integral is zero.


Tags 
calculating, probabilities 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Calculating probabilities  help please  thanks  marshallp  Algebra  3  November 17th, 2016 03:41 AM 
Calculating probabilities from zscores  wubs23  Probability and Statistics  1  February 3rd, 2015 05:26 AM 
Who rocks probabilities? Calculating the odds of being caught in the act. :P  tmjames  Probability and Statistics  4  September 18th, 2014 10:45 AM 
composed probabilities and total probabilities  RifkiNada  Algebra  2  November 24th, 2012 03:32 AM 
Calculating Probabilities of Occurrences  CBSte  Algebra  1  July 8th, 2009 01:48 PM 