Question

57X55/56+27X27/28用简便方法怎样算

57X55/56+27X27/28用简便方法怎样算

Answer 1

57×55/56+27×27/28
=(56+1)×55/56+(28-1)×27/28
=56×55/56+1×55/56+28×27/28-1×27/28
=55+55/56+28-27/28
=(55+28)+(55/56-54/56)
=83+1/56
=83又56分之1
这种一般就是凑数，将a改写为(a+1)-1或者（a-1)+1

Answer 2

57X55/56+27X27/28=(56+1)*(56-1)/56+(28-1)^2/28=(56^2-1)/56+(28^2-2*28+1)/28=56-1/56+28-2+1/28=30+(1+2)/56=30又3/56

Answer 3

a^2-1=(a+1)(a-1)

57*55=56^2-1
27^2=26*28+1
原式=(56^2-1)/56+(26*28+1)/28
=56-1/56+26+1/28
=82+1/56
=82又1/56

Answer 4

57×55/56+27×27/28
=(56+1)×55/56+(28-1)×27/28
=56×55/56+1×55/56+28×27/28-1×27/28
=55+55/56+28-27/28
=(55+28)+(55/56-54/56)
=83+1/56
=83又56分之1

Answer 5

57X55/56+27X27/28
=（56+1）X55/56+（28-1）X27/28
=56X55/56+55/56+28X27/28-27/28
=55+55/56+27-27/28
=82+1/2