19又13/14*（-10）
=(20-1/14)*(-10)
=-10*20+1/14*10
=-200+5/7
=-199又2/7
57*55/56+27*27/28
=(56+1)*55/56+(28-1)*27/28
=56*55/56+55/56+28*27/28-1*27/28
=55+55/56+27-27/28
=82+1/56
=82又1/56
-13*2/3-0.34*2/7+1/3*（-13）-5/7*0.34
=-13*(2/3+1/3)-0.34*(2/7+5/7)
=-13*1-0.34*1
=-13.34