= 1- 1/6=5/6

② One and a half+two and a sixth+three and a twelfth+...+twenty and a quarter.

= 1+2+3+....+20+ 1/ 1×2+ 1/2×3+ 1/3×4+....+ 1/20×2 1

=﹙ 1+20﹚×20/2+ 1- 1/2+ 1/2- 1/3+....+ 1/20- 1/2 1

=2 10+ 1- 1/2 1

=2 10 and 20/2 1

(3) 1 times 2/3+2 times 2/3+3 times 2/4+4 times 2/5+...+ 98 times 299+99 times 200%.

=2×﹙ 1- 1/ 100﹚

=99/50

(4) One and a half times+two and a third times+three and a quarter times+four and a fifth times +...+98 and 98 times one ninth.

= 1+2+3+......+98+ 1- 1/99

=﹙ 1+98﹚×98/2+98/99

=485 1 and 98/99