
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
July 25th, 2018, 07:04 AM  #1 
Member Joined: Sep 2014 From: Sweden Posts: 94 Thanks: 0  Calculate probability of interval with a random variable?
Hi! I have studied algebra and calculus mostly (Calculus 1), not so much probability. So my problem is that I have a random variable called r that can generate any number from 1 to 100 (1 and 100 are included, interval [1, 100]). I set up a condition that if r >= 1 and r <= 75 then generate a wood, stone or metal block, but if r >= 75 and r <= 100 then generate a emerald, ruby or diamond block. So in the first condition (interval) there is a greater chance of generating some of these blocks than there is in the second condition (interval), I assume, but how can I calculate the probability of the interval? Or calculate the interval to get a certain probability? I already know that I want a 75% chance for the easier blocks to generate and 25% for harder blocks to generate. Last edited by DecoratorFawn82; July 25th, 2018 at 07:08 AM. 
July 25th, 2018, 07:36 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,307 Thanks: 1976 
Does the value of r have to be a whole number?

July 25th, 2018, 09:30 AM  #3 
Member Joined: Sep 2014 From: Sweden Posts: 94 Thanks: 0 
Yes, the number r is always an integer.

July 25th, 2018, 09:41 AM  #4 
Senior Member Joined: Sep 2015 From: USA Posts: 2,320 Thanks: 1232 
We have to assume that $r$ is a uniform random variable in the absence of any other information regarding it's distribution. We also have to correct your conditions a bit assuming we never generate two blocks. I'm going to assume you generate the harder blocks if $75 < r \leq 100$, i.e. $r=75$ generates a block in the first group, not the second. Given this assumption we can compute the probability of wood, stone, or metal as $P[\text{wood, stone, metal}] = \dfrac{\text{number of values of }r \text{, such that }1 \leq r \leq 75}{\text{total possible values of }r} = \dfrac{75}{100} = \dfrac 3 4$ 
July 25th, 2018, 09:49 AM  #5 
Member Joined: Sep 2014 From: Sweden Posts: 94 Thanks: 0 
Yeah, that probably is the better assumption. Thanks for helping out .


Tags 
calculate, interval, probability, random, variable 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
How can I calculate the joint probability for three variable?  Ashikandi  Advanced Statistics  0  June 5th, 2018 01:00 AM 
Binomial random variable probability  alw15625  Probability and Statistics  1  October 30th, 2015 03:32 PM 
Probability to find the random variable X within an interval  Linder88  Probability and Statistics  1  October 28th, 2015 07:48 PM 
probability at a point for a continuous random variable  rsashwinkumar  Advanced Statistics  3  January 7th, 2013 04:25 PM 
random variable probability  meph1st0pheles  Advanced Statistics  0  February 22nd, 2010 07:27 PM 