1/1x2+1/3x4+1/5x6+1/7x8+1/9x10=?不要死算,

Question

1/1x2+1/3x4+1/5x6+1/7x8+1/9x10=?不要死算,

Answer 1

1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10
=1-1/2+1/2-1/3+1/3-.-1/9+1/9-1/10
=1-1/10
=9/10