
Advanced Statistics Advanced Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
February 17th, 2014, 02:12 AM  #1 
Senior Member Joined: Feb 2014 Posts: 114 Thanks: 1  Fourdigit number
Hi, How many fourdigit number which each digit smaller than previous digit? 
February 17th, 2014, 02:22 AM  #2 
Math Team Joined: Apr 2010 Posts: 2,778 Thanks: 361  Re: Fourdigit number
Also posted here: viewtopic.php?p=193943#p193943 You can pick 10 digits (you won't get a leading 0). You want them all distinct, since the next digit is smaller then the preceding. For the first digit, you have 10 choices. AND for the second digit, you have 9 choices, given that you can't pick the one you already picked AND for the third digit, you have 8 choices, given that you can't pick the ones you already picked AND for the fourth digit, you have 7 choices, given that you can't pick the ones you already picked Due to the AND's, you may multiply the amount of choises. Gives 10 * 9 * 8 * 7. The four digits are distinct. Four distinct digits can be sorted in 4 * 3 * 2 * 1 = 24 ways. So divide by 24. Gives 10 * 9 * 8 * 7 / (4 * 3 * 2 * 1) = 
February 17th, 2014, 04:24 AM  #3 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,103 Thanks: 907  Re: Fourdigit number
3210 ... 9876 : 210 1234 ... 6789 : 126 

Tags 
fourdigit, number 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Fourdigit number  life24  Number Theory  8  February 20th, 2014 10:16 AM 
Number system  proving 9 digit number not divisible by 5  sachinrajsharma  Number Theory  7  April 29th, 2013 05:49 AM 
A=abc=a !+b !+c ! (A is a 3digit number)  Albert.Teng  Algebra  10  November 8th, 2012 11:25 AM 
tendigit number  Albert.Teng  Algebra  6  July 21st, 2012 11:30 PM 
Finding two digit number  stevecowall  Algebra  2  January 4th, 2012 07:44 PM 