# Probability Question Help :(

• Aug 5th 2008, 01:57 PM
ManiacBR
Probability Question Help :(
I've been giving a bunch of probability questions to do, and I've been struggling over this one for a while.

Hoping you guys can help me out.

One in 40 cars of a particular type may develop a fault while under a gaurentee. 12 of these cars are sold. Calculate the probability that:
(i) 0
(ii) 1
(iii) 2 or more

of these 12 cars will be returned for repair while under gaurentee.

I'd tell you some of the things id treid but they're all completey off the mark.

Any help appreciated.

• Aug 5th 2008, 02:02 PM
TKHunny
You can be expected to recognize a Binomial Distribution and calculate Binomial Probabilities.

Recognize:

n = 12
p = 1/40= Probability of Fault Under Guarantee
q = 1-p = 39/40

Calculate:

\$\displaystyle Pr(0) = 1*q^{12}*p^{0}\$
\$\displaystyle Pr(1) = 12*q^{11}*p^{1}\$

You do Pr(2).

Note: Pr(2) is just for practice. You don't need it to answer the question, since Pr(2 or more) = 1 - Pr(0) - Pr(1)
• Aug 6th 2008, 11:21 AM
ManiacBR
Thanks for the help, i've got it all done now :)

Cheers