Author 
Topic 

reather
Junior Member
USA
3 Posts 
Posted  03/18/2012 : 12:35:41

I need help trying to find the probability of an answer can you help me. the question is. selecting a committee. a parentteacher committee consisting of 4 people is to be formed from 20 parents ans 5 teachers. find the probability that the committee will consist of these people.( all teachers)b( 2 teachers and 2 parents)c ( all parents) d (1 teacher and 3 parents). i need to know which formula to use and how to set it up. 


Ultraglide
Advanced Member
Canada
299 Posts 
Posted  03/19/2012 : 12:02:21

You didn't show any work so I'll give you a couple of hints. How many committees of four can be formed from 25 people? How many committees of four can be formed from five teachers? 


reather
Junior Member
USA
3 Posts 
Posted  03/19/2012 : 19:32:38

quote: Originally posted by Ultraglide
You didn't show any work so I'll give you a couple of hints. How many committees of four can be formed from 25 people? How many committees of four can be formed from five teachers?
6 


reather
Junior Member
USA
3 Posts 
Posted  03/19/2012 : 19:33:42

quote: Originally posted by reather
quote: Originally posted by Ultraglide
You didn't show any work so I'll give you a couple of hints. How many committees of four can be formed from 25 people? How many committees of four can be formed from five teachers?
6
1 


the_hill1962
Advanced Member
USA
1468 Posts 
Posted  03/22/2012 : 12:15:33

Good hint, Ultraglide. I am not very good with probabilities and I stumbled when I tried to help with this question. I see that reather answered "6" to your question "How many committess of four can be formed from 25 people". Is reather correct? I don't think so. Aren't you supposed to use the combination formula _{n}C_{r} = n!/[r!(nr!)] ? If so, then the answer to your question "How many committess of four can be formed from 25 people" is _{25}C_{4} and that is 25*24*23*22*21*20*19*18*17*16*15*14*13*12*11*10*9*8*7*6*5*4*3*2*1 (4*3*2*1)(21*20*19*18*17*16*15*14*13*12*11*10*9*8*7*6*5*4*3*2*1) and that reduces to 25*24*23*22) 4*3*2*1 which is 12650. And for your second hint "How many committees of four can be formed from five teachers?", that would be _{5}C_{4} = 5 So the answer to the original question of what the probability of the committee having all teachers is 5/12650 = 1/2530 isn't it?

Edited by  the_hill1962 on 03/22/2012 12:25:05 


Ultraglide
Advanced Member
Canada
299 Posts 
Posted  03/24/2012 : 11:00:57

Yes, that is correct. 


Ultraglide
Advanced Member
Canada
299 Posts 
Posted  03/24/2012 : 19:33:49

For the two teachers and two parents:
How many ways can we choose two teachers? Now FOR EACH OF THESE WAYS we can choose two parents. This means that we find the product of these two cases to find the number of committees with two of each. 


the_hill1962
Advanced Member
USA
1468 Posts 
Posted  03/28/2012 : 11:21:19

Thanks. That makes sense. It is all starting to come back to me. 20 years since taking a probability course takes its toll! I got an A in the course but I didn't retain anything after the course was over! 


Ultraglide
Advanced Member
Canada
299 Posts 
Posted  03/28/2012 : 14:42:36

We all have our areas of expertise. The capitalized part was how my high school teacher emphasized the product. When I responded to the linear transformation in another section, I had to pull out my old text. I had forgotten the definition even though I taught it for many years. 


Tessa
Average Member
USA
14 Posts 
Posted  04/25/2012 : 00:10:10

hello the_hill1962 and Ultraglide! would you mind looking at my 2 new posts? I am having difficulty with them and I need really fast, reliable help as I am struggling severely with the question!!! Thank you!!! Tessa *that is my profile name* *my new posts are in the statistics part* 



Topic 
