It is known that there are an infinite number of worlds, but that not every one of them is inhabited, therefore there must be a finite number of inhabited worlds.

10 seconds sound clip from The Hitchhiker's Guide to the Galaxy (1981) - Episode 5 sitcom.

You can hear this line at 00:29:13.400 in the Blu-ray version of the TV Series.

Quote context

[...]

- Its simplistic style is partly explained by the fact that its editor, having to meet a publishing deadline, copied the information off the back of a packet of breakfast cereal.

- Hastily embroidering it with a few footnotes in order to avoid prosecution under the incomprehensibly torturous Galactic copyright laws.

- It is interesting to note that a later and wilier editor sent the book backwards in time through a temporal warp, and then successfully sued the breakfast cereal company, for infringement of the same laws.

- Here's a sample, in both headings and footnotes...

- The Universe. Some information to help you live in it. 1. Area: infinite. 2. Population: none.

- It is known that there are an infinite number of worlds, but that not every one of them is inhabited, therefore there must be a finite number of inhabited worlds.

- Any finite number divided by infinity is as near to nothing as makes no odds.

- So, if every planet in the universe has a population of zero, then the entire population of the universe must also be zero.

- And any people you may meet from time to time are merely the products of a deranged imagination.

- 3. Monetary units: none. In fact there are three freely convertible currencies in the galaxy, but the altairian dollar has recently collapsed.

[...]