# Probably 2 very easy probability problems

• May 13th 2008, 02:30 PM
Smifsret
Probably 2 very easy probability problems
Hi, I need help understanding 2 probability problems.

I have a box with 24 circuit boards and I know 5 are faulty, if I take out 6 boards what is the probability that one of those 6 is faulty?

I am unsure about the second one althought it seems very easy, almost to easy.

A medicine makes 0.07 sick, what is the probability that 3 out of 10 people that take it will get sick?

I have a hard time following the examples in the book so I hope you can shed some light on what seems to be 2 easy questions.

Thanks!
• May 13th 2008, 02:52 PM
galactus
The second one is a binomial probability.

$C(10,3)(\frac{7}{100})^{3}(\frac{93}{100})^{7}$
• May 13th 2008, 02:55 PM
galactus
The first one is a hypergeometric probability,

You choose 1 from the 5 faulty ones and 5 from the 19 good ones.

$\frac{C(5,1)C(19,5)}{C(24,6)}$
• May 13th 2008, 03:30 PM
Smifsret
Thank you but can you explain how to proceed from there?
• May 13th 2008, 04:01 PM
galactus
Run it through a calculator. C(10,3), for instance, means the number ways to choose 3 items out of 10. C(10,3)=120

The formula is $\frac{n!}{(n-k)!k!}=\frac{10!}{(10-3)!3!}=120$
• May 13th 2008, 04:26 PM
Smifsret
Ok now I feel even dumber, when I run that I get 4320.

Also, how do i get the % of 3 out of 10 if I even get 120?

Sorry to be such a bother.
• May 15th 2008, 02:09 AM
Smifsret