Page 113 - Fixtures

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3 8 [AIME 1990] ( )
3
.
. :
. ()
()

CBA .
.
. AAABBBCC

. 8! = 8 × 7 × 6 × 5 × 4 = 560
3!×3!×2! 3×2×2

ABCD [AIME 2004] ( )

.C < D B >C A<B
1423 1324
.

4. 9
.C(9, 4)