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解：$(1)$原式$=\frac {5y}{x^2}；$$(2)$原式$=-\frac a{2b}；$$(3)$原式$=-\frac {4m}{3n}$

解：$(4)$原式$=\frac x{2y}；$$(5)$原式$=-\frac {3x}{5y}；$$(6)$原式$=-\frac {x+y}{xy}$

解：$(1) \frac {3a^2-1}{1-a}=- \frac {3a^2-1}{a-1}；$$(2) \frac {x-x^2}{1+2x^2}=- \frac {x^2-x}{2x^2+1}；$$(3) \frac {-1+2x-x^2}{-2x+1}=\frac {x^2-2x+1}{2x-1}$

解：$(4) \frac {-a^2+a-1}{1-a-a^2}=\frac {a^2-a+1}{a^2+a-1}；$$(5) \frac {4-3x^2}{-x+2}=\frac {-(4-3x^2)}{-(-x+2)} =\frac {3x^2-4}{x-2}；$

$(6) \frac {x-1}{4x+1-2x^2}=\frac {x-1}{-(2x^2-4x-1)}=- \frac {x-1}{2x^2-4x-1}$

解：$(1)$原式$=\frac {10×(0.3a+0.5b)}{10×(0.2a-0.1b)}=\frac {3a+5b}{2a-b}$

$(2)$原式$=\frac {10×(0.2a+0.5b)}{10×(0.7a-b)}=\frac {2a+5b}{7a-10b}$

$(3)$原式$= \frac {12×(\frac 12a+\frac 23b)}{12×(\frac 12a-\frac 14b)}=\frac {6a+8b}{6a-3b}$

解：$(4)$原式$= \frac {30×(\frac 13x-0.2y)}{30×(\frac {1}{2} x+0.3y)}=\frac {10x-6y}{15x+9y}$

$(5)$原式$= \frac {30×(\frac {1}{3} x- \frac {1}{5} y)}{30×(2x+\frac 16y)}=\frac {10x-6y}{60x+5y}$

$(6)$原式$=\frac {100×(\frac {1}{100} x^2- \frac {1}{5} )}{100×(1.3x^2+0.24)}=\frac {x^2-20}{130x^2+24}$