Question

(+111)+(-101)+(91)+(-81)+...+(+31)+(-21)+(+11)+(-1)怎样巧算

Answer 1

(+111)+(-101)+(91)+(-81)+...+(+31)+(-21)+(+11)+(-1)

=(+111-101)+(91-81)+...+(+31-21)+(+11-1)

=10X6

=60