2008×2009分之2007
=(2009-1)×2009分之2007
=2009×2009分之2007-1×2009分之2007
=2007-2009分之2007
=2006又2009分之2
9999×7+1111×37
=1111×9×7+1111×37
=1111×63+1111×37
=1111×(63+37)
=1111×100
=111100
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