Tenpai Expansion – I Play Riichi

This section covers choosing the discard or discards from a tenpai hand that give you the largest wait to win. This entails checking possible waits given a number of slightly different hand makeups.

You should be familiar with an earlier Exam guide, Wait Determination, before you continue, as this guide uses the framework from that page to systematically determine the correct answer for these types of problems.

Tenpai Expansion Method

In this, you pull one tile from each available, quickly do Wait Determination on what is left, and make a note on the result. Once done, the largest wait is your answer. The second number , the number of different tile values you need, is there as a check-back, to help keep count as you calculate the first number.

Example: tile tile tile tile tile tile tile tile tile tile tile tile tile tile

First, set up the Wait Determination array. Above each column, instead of putting the number of the wait, you’ll be putting the number of tiles in that wait (outs) and the number of different waits (types). An example will be given shortly.

We start by “discarding” a tile . This quickly resolves to a 2-sided tile tile wait. there are 4 tile , and 3 tile left, so this is a 7 tile wait, on 2 different tiles: 7-2.

Discarding a tile leaves you not tenpai..

Same with a tile ..

Discarding a tile leaves you with the same 2-sided tile tile wait. 7 tiles, 2 types, 7-2.

If you find it hard to keep track, you can do a row for each tested tile, to help keep things orderly. (Make your notes from the bottom of the paper so there is room). Here is an example:

Discarding a tile leaves with with a single wait on tile (the example has it as the pair: you could also have it as a kanchan-style 6_8). There are 2 of them gone, so it is 2 tiles, 1 type, 2-1.

Discarding a tile can be seen as 2 different waits: a tile tile wait, and a tile wait. 2 of those 12 tiles are gone, so this is a 10 tile, 3 type wait. 10-3.

Lastly, discarding an tile leaves a double-pair wait, tile tile . 4 gone, 4 left, so 4 tiles, 2 types, 4-2.

That is all the possible discards. Looking through them, the tile wait is the largest, and so the answer is 7p. (If another tile had the same number of “outs” but more “types”, so like 10-4 or 10-5, you would list it in your answer as well)

A Warning about Time

Note that this method takes a bit of time. I strongly suggest you leave these sections for last – usually, there are other sections after this on the test with questions of equal value that you can solve much more quickly. Do those first and come back.