# Probabilty issues..

• May 6th 2009, 01:31 PM
puzzledwithpolynomials
Probabilty issues..
Of 7 kittens in a litter, 4 have stripes. Three kittens are picked at random. Find the odds of each event.
1) All three have stripes.
2) Only 1 has stripes.
3) One is not striped.
I am just...utterly stuck. I tried doing 4 CR 3/7 CR 4 for the first one, but that's apparently not correct..
• May 6th 2009, 01:52 PM
awkward
Quote:

Originally Posted by puzzledwithpolynomials
Of 7 kittens in a litter, 4 have stripes. Three kittens are picked at random. Find the odds of each event.
1) All three have stripes.
2) Only 1 has stripes.
3) One is not striped.
I am just...utterly stuck. I tried doing 4 CR 3/7 CR 4 for the first one, but that's apparently not correct..

puzzled,

You are very close.

There are $\binom{7}{3}$ ways to pick the three kittens, all of which are equally likely. Of these, there are $\binom{4}{3}$ combinations which result in three striped. So the probability is ...
• May 6th 2009, 02:14 PM
puzzledwithpolynomials
4/35?
• May 6th 2009, 03:59 PM
awkward
Quote:

Originally Posted by puzzledwithpolynomials
4/35?

Right!