@ @SU@ @óïbÿa@‡ÉÜa@ú†bjà@ @ . 18 3 . 3 18 − 6 = 12 18 . .1000 1 .18 ×12 = 216 [PACAT] ( ) 7 ABC 1000 7 7 . 999 1 : . A,B,C ∈ {0,1,2,…,9} 217 78 17 7 7 () 7 CBA . 743 A7 . 9 × 9 = 81 . 3 × 81 = 243 .C B .7 () .9 7 C BA 7