My Math Forum  

Go Back   My Math Forum > High School Math Forum > Probability and Statistics

Probability and Statistics Basic Probability and Statistics Math Forum


Reply
 
LinkBack Thread Tools Display Modes
March 14th, 2011, 11:11 PM   #1
Newbie
 
Joined: Aug 2009

Posts: 29
Thanks: 0

How can I understand permutation and probability question?

Especially on probability question. I found it difficult to understand a question that asked for its probability whether using permutation or combination.

Example of final exam question:
Quote:
Find the number of integers between 1000 and 4000 which can be formed by using the digits 1,2,3 and 4.
i) if each digit may be used only once
ii) if each digit may be used more than once
Is there any 'way' I can instantly understand this kind of question? Because each time I stumble upon this kind of question, I usually get confused what to used, Permutation, combination or factorial?
xdeathcorex is offline  
 
March 14th, 2011, 11:27 PM   #2
Senior Member
 
MarkFL's Avatar
 
Joined: Jul 2010
From: St. Augustine, FL., U.S.A.'s oldest city

Posts: 12,211
Thanks: 521

Math Focus: Calculus/ODEs
Re: How can I understand permutation and probability questio

For i) we have 4 choices for the first digit, 3 for the 2nd 2 for the 3rd and 1 for the 4th:



For ii) we have 4 choices for all 4 digits:

MarkFL is offline  
March 15th, 2011, 01:56 AM   #3
Senior Member
 
Joined: Feb 2009
From: Adelaide, Australia

Posts: 1,519
Thanks: 3

Re: How can I understand permutation and probability questio

Oops! You don't have four choices for the first digit; it can only be 1, 2, or 3. So you have (i) 18, and (ii) 192.

The question you have to ask yourself is, "How are the valid possibilities constructed?"
Can you construct them by permuting a list? Then think about permutations.
Can you construct them by choosing from a list? Then think about combinations.
Is it possible to select one element at a time, without any selection having an impact on later selections? Then think about a multiplication.
If one selection does affect later selections, consider drawing a game tree of possibilities.
aswoods is offline  
March 15th, 2011, 05:49 AM   #4
Senior Member
 
MarkFL's Avatar
 
Joined: Jul 2010
From: St. Augustine, FL., U.S.A.'s oldest city

Posts: 12,211
Thanks: 521

Math Focus: Calculus/ODEs
Re: How can I understand permutation and probability questio

D'oh!
MarkFL is offline  
Reply

  My Math Forum > High School Math Forum > Probability and Statistics

Tags
permutation, probability, question, understand



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
permutation probability problem,,, hamburgertime Probability and Statistics 2 April 10th, 2013 02:35 PM
simple question, but can't understand the solution..... mathmaniac Advanced Statistics 17 February 25th, 2013 11:58 PM
Another maximum question I don't understand Math4dummy Algebra 7 April 15th, 2012 11:01 PM
Probability question I don't understand sneaky Probability and Statistics 3 September 23rd, 2010 10:41 PM
Permutation probability springgengxin Advanced Statistics 0 June 14th, 2010 01:56 PM





Copyright © 2019 My Math Forum. All rights reserved.