Simple combinatorics q

  • Thread starter catalyst55
  • Start date
24
0
The question goes something like this...

What is the probability of an E being one of the 4 randomly chosen letters from the word ENERGISE?

This is how i did it (the book says its wrong):

ENERGISE ==> 3 Es, 5 Non-Es (partitioning)

hence: (3c1*5c3)/(8c4)

the book has 55/56....

Cheers
 
217
0
catalyst55 said:
the book has 55/56....
I don't see how they came up with that answer....I think your answer is correct.

(note 8C3 is 56...why would the book have that?)
 

Gokul43201

Staff Emeritus
Science Advisor
Gold Member
6,987
14
Catalyst : I suggest you write down the question exactly as it appears. There are two similar looking possibilities : (i) the probability that there is EXACTLY 1 E among 4 randomly chosen letters , and (ii) the probability that there is AT LEAST 1 E among the 4 letters.

PS : You have answered assuming the first case. If that is the right case, then your answer is correct. Notice that the book's answer = 1 - your answer. If it is the second case, the book's answer is still wrong.
 
217
0
Gokul43201 said:
Notice that the book's answer = 1 - your answer.

Why do you say that? catalyst55's answer is 3/7....1-3/7=4/7. :confused: Am I missing something here?????? :redface:
 

Gokul43201

Staff Emeritus
Science Advisor
Gold Member
6,987
14
No, you're not. I'm just losing it slowly... :biggrin:

My bad there. I must have forgotten how to multiply ! :redface:
 
24
0
Gokul43201 said:
Catalyst : I suggest you write down the question exactly as it appears. There are two similar looking possibilities : (i) the probability that there is EXACTLY 1 E among 4 randomly chosen letters , and (ii) the probability that there is AT LEAST 1 E among the 4 letters.
Hey Gokul43201,

I've thought about that and ive concluded that its definitely the former -- either way the answer on the back is wrong.

I've also asked my teacher and he's confirmed this.

Thanks a lot for your help guys.
 

Related Threads for: Simple combinatorics q

Replies
22
Views
1K
  • Posted
Replies
3
Views
6K
  • Posted
Replies
1
Views
1K
Replies
2
Views
2K
  • Posted
Replies
5
Views
1K
  • Posted
Replies
9
Views
956
  • Posted
Replies
4
Views
717
  • Posted
Replies
8
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top