Look to the best final form

 

Answer

Commentary

Look to the best final form

On a similar theme of  All simples or Flat hand?? 

3m is the worst,  because you loss the accpeptance of 3s and 4s.

If you draw these tiles, you can call for Riichi of waiting for 1-4m.

So this main theme is this comparison,

this final form for all simples ??

or  this final form for flat hand ??

If you discard 7m, this hand has acceptance of 2 3 4 5s  ＋ 2 5 8m ＋3 6m. (Except for the case of 1 4m drawing, because bad wating). 

If you discard 5m, this hand has acceptance of 2 3 4 5s  ＋ 1 4 7m ＋3 7m.

Considering calling, to discard 7m is able to calling 2 5s and ready for waiting  2 5 8m.

To discard 5m is able to calling 3 7m (for Pong), or 4 7m(for chow) and ready for  wating 2 5s. 

In this case, you can't call for 2 5s, because if you take 1 4 7m wating, you can't  win by 1m.

So 7m is superior to 5m. 

 In many cases, it is easier to win if you look to ALL simples.

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