Binomial distribution

  • Thread starter TyErd
  • Start date
  • #1
TyErd
299
0

Homework Statement


I've uploaded a picture of the question.
I need help in identifying the correct number of trials, probability of success and the X value(number of successes)

Homework Equations


i'm using the binomial distribution function on the calculator but I've attached the formula just in case


The Attempt at a Solution


I used n=7, p=7/15 and X=7 which yields me a probability of 0.00482 which is incorrect. The correct answer is 0.000155 but not sure how.
 

Attachments

  • 11111111111111111111111111111.png
    11111111111111111111111111111.png
    7.8 KB · Views: 331
  • WindowsLiveWriterBinomialdistribution_B2A9binomialdist.png
    WindowsLiveWriterBinomialdistribution_B2A9binomialdist.png
    8.6 KB · Views: 368

Answers and Replies

  • #2
LCKurtz
Science Advisor
Homework Helper
Insights Author
Gold Member
9,568
774

Homework Statement


I've uploaded a picture of the question.
I need help in identifying the correct number of trials, probability of success and the X value(number of successes)

Homework Equations


i'm using the binomial distribution function on the calculator but I've attached the formula just in case


The Attempt at a Solution


I used n=7, p=7/15 and X=7 which yields me a probability of 0.00482 which is incorrect. The correct answer is 0.000155 but not sure how.

The binomial distribution is inappropriate for this problem. You aren't doing independent trials with replacement. Think about how many ways you can select 7 cars from the 15 and how many ways you can select the 7 fwd cars.
 
  • #3
Dick
Science Advisor
Homework Helper
26,263
621
That's not a correct formula to use. How many ways are there to choose 7 cars from 15? Only one of those choices gives you all four wheel drives.
 
  • #4
TyErd
299
0
ahh, that's why i keep getting it wrong. Thanks, but if its not binomial, what is it?
 
  • #5
Dick
Science Advisor
Homework Helper
26,263
621
It's combinatorics. How many ways to select 7 objects from 15 objects?
 
  • #6
Ray Vickson
Science Advisor
Homework Helper
Dearly Missed
10,706
1,722
ahh, that's why i keep getting it wrong. Thanks, but if its not binomial, what is it?

It is the so-called hypergeometric distribution.

Note: instead of a combinatorial argument there is another way to get the correct answer. The probability that the first car is fwd is 7/15; that leaves 14 cars, of which 6 are fwd. So (given the first is fwd) the probability that the second is fwd is 6/14, etc, etc.

RGV
 

Suggested for: Binomial distribution

Replies
7
Views
1K
  • Last Post
Replies
16
Views
640
Replies
15
Views
1K
Replies
4
Views
667
Replies
7
Views
499
Replies
3
Views
509
  • Last Post
Replies
4
Views
1K
Replies
17
Views
698
Replies
4
Views
1K
Top