Replacement and Without Replacement

Bob and Laquisha have volunteered to serve on the Junior PromCommittee. The names of twenty volunteers, including Bob and Laquisha, are put into a bowl. If two names are randomly drawn fromthe bowl **without replacement**, what is the probability that Bob’s name will be drawn first and Laquisha’s name will be drawn second?

My Work:

Let Bob = 1

Let Laquisha = 1

There are 20 volunteers.

I then decided to multiply (1/20) (1/20).

However, the correct answer is (1/20) (1/**19**)

Where did **19 **comes from?

Also, what is the difference between replacement and without replacement probability questions?

Is there a simple formula for the two?