
Advanced Statistics Advanced Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
May 18th, 2010, 12:25 PM  #1 
Newbie Joined: Apr 2010 Posts: 4 Thanks: 0  Expectation and Variance Question
Hi, Can anyone help answering this question?? A college which has 120 male and 90 female students organizes an endofyear ball. Each male student has, independently, probability 0.7 of going to the ball. The corresponding probability for females is 0.9. Males and females at the ball pair off until there is noone of the opposite gender available. What is the expectation and variance for the number of males at the ball without a female partner? What extra assumption do you need to make in answering this question? Thanks, 
May 18th, 2010, 01:13 PM  #2 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: Expectation and Variance Question
I get 13317914063183385152860742783713884725505010780166 72941997421755502667043210319640026719898824512636 38117452486544321470918809794832999512051913359073 09200707328415063814731244325594255095795476112477 72869669129075091300415910023598148580585456068528 0418074276117710255341/17632428509737537813642539535622820786902183233659 51365531331978947023821789340949272397231859649884 32310482214413697945577339443852406950188546640658 35006250000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 000000000000 with Code: sum(m=0,120,binomial(120,m)*(7/190)^m*(3/10)^(120m)*sum(f=0,120,max(mf,0)*binomial(90,f)*(9/10)^f*1/10^(90f))) Code: sum(m=0,120,binomial(120,m)*(7/190)^m*(3/10)^(120m)*sum(f=0,m1,(mf)*binomial(90,f)*(9/10)^f*1/10^(90f))) 

Tags 
expectation, question, variance 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Expectation, Variance, Covariance  mahjk17  Advanced Statistics  0  November 19th, 2012 08:34 AM 
Expectation and Variance... HLP!  Juliayaho  Advanced Statistics  1  October 1st, 2012 10:53 AM 
Expectation and Variance  thekiterunner  Advanced Statistics  3  August 10th, 2011 12:16 PM 
Expectation and Variance Question  hendaz  Algebra  2  May 23rd, 2010 01:57 PM 
Conditional Expectation and Variance Question  nibblebot  Advanced Statistics  1  October 30th, 2007 12:05 PM 