Letters & Numbers is the short-lived Australian version of the successfully long-running UK game show Countdown which in turn was based on the long-running French game show Des chiffres et des lettres ("Numbers & Letters").
Two contestants compete against each other in a series of nine rounds, split into three sections. The first two sections consist of two letters rounds followed by a numbers round; the third section consists of a letters round, a numbers round, and the conundrum round. After the first commercial break, Astle would present a story on the origins of particular words and phrases.
One contestant chooses how many vowels and consonants they would like to make up nine randomly chosen letters. There must be at least three vowels and four consonants. The contestants then have thirty seconds to find the longest word that they can make out of these letters. Any word which appears in the Macquarie Dictionary is allowable, as well as some inflections. The contestant with the longest word is awarded one point for each letter in the word, but nine-letter words count double (thus scoring 18 points). If both contestants find words of equal length then each is awarded points.
One contestant chooses how many "small" and "large" numbers they would like to make up six randomly chosen numbers. Small numbers are between 1 and 10 inclusive, and large numbers are 25, 50, 75, or 100. All large numbers will be different, so at most four large numbers may be chosen. The contestants have to use arithmetic on some or all of those numbers to get as close as possible to a randomly generated three-digit target number within the thirty second time limit. Fractions are not allowed—only integers may be used at any stage of the calculation.
For numbers selections, they are to be straightforward. The numbers are always placed in a fixed order (going Right to Left - Small numbers are placed first, then the large ones).
Points are awarded for the closest solution, and again both contestants score if the solutions are equally close. 10 points are given for an exact answer, 7 points for a non-exact solution up to 5 from the target, and 5 points for a solution between 6 and 10 from the target. If neither contestant can get within 10, no points are awarded.
A nine-letter anagram made up of two smaller words is given to the contestants who must unscramble the word within the time limit of thirty seconds. The first person to buzz in and correctly identify the word wins 10 points. If a contestant answers incorrectly then they may not guess again and the other contestant has the remaining time to attempt to find the answer. If neither contestant buzzes in with a correct answer during the time limit then no points are awarded. In the event that the trailing player is 10 or less behind. The Conundrum became crucial and the set was darkened. If the scores are tied after the conundrum, tie-breaker conundrums are used until the match is decided.
The winner of the game returns in the next show to face a new opponent; a player who wins six times is forced to retire, becoming a retired champion, in which case two new contestants will play the next game. Retired champions with the highest cumulative score may return for a special tournament at the end of each series. Every contestant also wins a Macquarie Dictionary 5th Edition, signed by the presenters.
Before the commercial break, the audience is given a "Word Mix"—an 8 letter anagram similar to the conundrum, but accompanied by a verbal clue. At the end of the break the anagram is revealed. This does not count towards the scores of the contestants.