Question

2×4分之一+4×6分之一+6×8分之一+.198×200分之一

Answer 1

原式=1/4[1/(1*2)+1/(2*3)+1/(3*4)……+1/(99*100)]

=1/4[(1-1/2)+(1/2-1/3)+(1/3-1/4)+……+(1/99-1/100)]

=1/4(1-1/100)

=1/4*(99/100)

=99/400