解:依据题意有,
66*77+77*88+88*99
=11*11(6*7+7*8+8*9)
=11*11(42+56+72)
=121*170
=121*(100+70)
=12100+8470
=20570
66x77+77x88+88x99
=11x11x(6x7+7x8+8x9)
=11x11x(42+56+72)
=11x11x170
=121x170
=121x200 -121x30
=24200-3630
=20570
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