# Thread: homework and statistics help? Can someone help me out with these 2 questions please

1. ## homework and statistics help? Can someone help me out with these 2 questions please

Ok so im Having a pretty hard time with this statistics course im taking I keep getting stuck and now i'm stuck on these 2 questions can someone please let me know how to do these and maybe a bit of info on why this is the way its done. just trying to make sense of this. I'd like to solve the questions on my own just trying to figure out what formula and how to know when I should use which formula. Also if anyone knows of any websites that have some good good basic business statistics learning info please let me know, my text book is not very helpful. Thanks!!

7. Thirty percent of the workers in company XYZ take public transportation daily to go to work. In a sample of ten workers, what is the probability that (6 marks)

1. four workers take public transportation to work daily?

1. at most, two people take public transportation to work daily?

1. at least three people take public transportation to work daily?

8. Customers arrive at a particular ATM at the rate of 30 customers per hour.
(6 marks)

1. What is the probability of three customers arriving in a five minute-time interval?

1. What is the probability of at least three customers arriving in a five-minute interval?

1. What is the probability of no customers arriving in a five-minute interval?

2. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Well question 7 is a Binomial distribution with n = 10 and p = 0.3

If we say that P is the distribution of public transport users, can you work out \displaystyle \begin{align*} \textrm{Pr}\, \left( P = 4 \right) , \textrm{ Pr}\, \left( P \leq 2 \right) , \textrm{ Pr}\, \left( P \geq 3 \right) \end{align*}?

3. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Originally Posted by Prove It
Well question 7 is a Binomial distribution with n = 10 and p = 0.3

If we say that P is the distribution of public transport users, can you work out \displaystyle \begin{align*} \textrm{Pr}\, \left( P = 4 \right) , \textrm{ Pr}\, \left( P \leq 2 \right) , \textrm{ Pr}\, \left( P \geq 3 \right) \end{align*}?

darn, i dont think thats anywhere near what i got. after a bit of research (before seeing your reply) This is what i had. I have no idea where to start with what youve given me . I feel like i must have missed an entire math course as a prerequisite or something because it all just looks like gibberish

n!
P (X)=---------- *(p)x*(Q)n-x
(n-x)!X!

N!/(n-x)! X!
10!/((10-4)! *4!)

3628800/((6!)*24)
3628800/720*24
3628800/17280
=210

P=30% or.30
Q=100%-30% or .70

P4=0.0081

Q(.7-4)

.7(10-4)
.76
=0.117649

210*0.0081*0.117649
=0.20012 or 20.012%

am I completely off?

anyone?

5. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Originally Posted by steen
anyone?
I can't understand what you've done at all.

As ProveIt noted this is a binomial distribution with parameters n=10, and p=0.3

This is given by the formula

$Pr[k]=\begin{pmatrix}10 \\ k\end{pmatrix} p^k (1-p)^{10-k}$

for i) just evaluate this at k=4

for ii) find the sum of these probabilities for k=0,1,2

for iii) at least 3 is the complement of at most 2, so simply subtract the value you obtained in (ii) from 1

8) This is a very similar problem but it is now the Poisson distribution with parameter $\lambda=30$

read up on the Poisson distribution and apply similar methods as I did in problem 7.

6. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Thanks for your info i m pretty sure I must have skipped a prerequisite class because I have no idea what to do with the numbers you've given me even after reading up . would I just plug 4 into all of the k spots in the formula?
Originally Posted by romsek
I can't understand what you've done at all.

As ProveIt noted this is a binomial distribution with parameters n=10, and p=0.3

This is given by the formula

$Pr[k]=\begin{pmatrix}10 \\ k\end{pmatrix} p^k (1-p)^{10-k}$

for i) just evaluate this at k=4

for ii) find the sum of these probabilities for k=0,1,2

for iii) at least 3 is the complement of at most 2, so simply subtract the value you obtained in (ii) from 1

8) This is a very similar problem but it is now the Poisson distribution with parameter $\lambda=30$

read up on the Poisson distribution and apply similar methods as I did in problem 7.

7. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Yes, and p = 0.3

8. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Thank you! I think k I'm going to read up on how to solve the problem I've never seen the 10 over k in giant bracket's before and I don't know how to solve that I think that's what I'm getting confused about the most.

9. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

Originally Posted by steen
Thank you! I think k I'm going to read up on how to solve the problem I've never seen the 10 over k in giant bracket's before and I don't know how to solve that I think that's what I'm getting confused about the most.
This is known as "10 choose k", also called the binomial coefficient of (10,k). It's given by

$\begin{pmatrix}n \\ k\end{pmatrix}=\dfrac {n!}{k!(n-k)!}$

and in the case of $n=10$

$\begin{pmatrix}10 \\ k\end{pmatrix}=\dfrac {10!}{k!(10-k)!}$

Do you know what $n!$ means?

10. ## Re: homework and statistics help? Can someone help me out with these 2 questions pl

N! Is a factorial? So if n were 5 n! Would b 5*4*3*2*1.