9又2000/2001×1949
=(10-1/2001)×1949
=10×1949-1949/2001
=19490-1949/2001
=19489+(2001/2001-1949/2001)
=19489+52/2001
=19489又52/2001
1/4÷[(1/4+11/20)×3/4+0.05]
=1/4÷(1/4×3/4+11/20×3/4+1/20)
=1/4÷(3/16+33/80+1/20)
=1/4÷(15/80+33/80+4/80)
=1/4÷52/80
=1/4÷13/20
=1/4×20/13
=5/13
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