Page 48 - Fixtures
P. 48

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        A∪B = A + B − A∩B

        10 ×10 ×10                 d1d2d3 = d4d5d6           10

           . B = 104  . A = 104 d7

                                            A ∩ B = 10

                                      .d1 = d2 =             = d7
        . A ∪ B = 104 + 104 − 10 = 19990

        x [AIME 1993] ( )

                                            4000 ≤ x < 7000

        A=5 A=4       ABCD

D = 6 D = 2 D = 0 )D                                  .A = 6
     .C 7 B
                                          4 A=4
        .1× 5 × 8 × 7
                   .1× 4 × 8 × 7      8 (D = 8
                                  .1× 4 × 8 × 7

                                                    A=5

                                            A=6

        .1× 4 × 8 × 7 + 1× 5 × 8 × 7 + 1× 4 × 8 × 7 = 728
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