Question

1*2\2005+2*3\2005+3*4\2005+4*5\2005+.+2004*2005\2005=等于多少?

Answer 1

2005*(1/(1*2) + 1/(2*3) + .+ 1/(2004*2005))

= 2005*(1 - 1/2 + 1/2 - 1/3 + .+ 1/2005)

= 2005*(1 - 1/2005)

= 2005 - 1

= 2004