# Binomial distribution

## 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.

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LCKurtz
Homework Helper
Gold Member

## 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.

Dick
Homework Helper
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.

ahh, thats why i keep getting it wrong. Thanks, but if its not binomial, what is it?

Dick
Homework Helper
It's combinatorics. How many ways to select 7 objects from 15 objects?

Ray Vickson