& gt 1/( 1*2)+ 1/(2*3)+ 1/(3*4)+ 1/(4*5)+……+ 1/(20 15*20 16)+ 1/(20 16*20 17)

=( 1- 1/2)+( 1/2- 1/3)+( 1/3- 1/4)+( 1/4- 1/5)+……+( 1/20 15- 1/20 / kloc-0/6)+( 1/20 16- 1/20 17)

= 1- 1/20 17=20 16/20 17

M= 1 (square)+1/2 (square)+1/3 (square) +...+20 16 (square)

& lt 1+ 1/( 1*2)+ 1/(2*3)+ 1/(3*4)+……+ 1/(20 14*20 15)+ 1/(20 15*20 16)

= 1+( 1- 1/2)+( 1/2- 1/3)+( 1/3- 1/4)+……+( 1/20 14- 1/20 15)+( 1/20 15- 1/20 16)

= 1+ 1- 1/20 16=403 1/20 16

This finale is beyond the outline, and it is ok as a competition question. As a mid-term exam question, I'm afraid the score rate is extremely low.