(10-10*4/55)+(9-9*4/55)+……(1-1*4/55)
=10-10*4/55+9-9*4/55+……1-1*4/55
=10+9+……1-10*4/55-9*4/55-……1*4/55
=(10+9+……1)-(10+9+……1)*4/55
=10(10+1)/2-[10(10+1)/2]*4/55
=55-55*4/55
=55-4
=51说一下简便方法