basic lotto question

Hi there,

I was always confused with combinations etc but in most cases I was able to find my way out. But this one is really annoying me:

Lotto game, possible numbers 1,2,...,49.
You play with 6 numbers.

What is the probability of actually getting all 6 correct?

Easy one, since the order does not matter (and no number can be picked twice) you find all possible combinations (=13983816) and the answer is 1/13983816.

Now how can you calculate the probability of getting 5 numbers correct.

I guess that finding all the combinations of 5 numers (let "a") and then claim that the answer is 1/a is not correct since you played with 6 numbers. That would only be correct if you played with 5 numbers.

Any help??

Thanx in advance for any answers!!!
Ok, just bumped in my head,

You calculate all possible combination of fives that a choice of six number can yield (let "b") and then claim that the answer is b/a correct. Correct!

Sorry guys I was just thinking for an hour for this before I send the message and really just came to me right after the post.

(Of course a little verification would not be bad!!)