Question

tính nhanh :1/12+1/20+1/30+............+1/90+1/110

Answer 1

1/12+1/20+1/30+...+1/90+1/110

=1/3.4+1/4.5+1/5.6+...+1/9.10+1/10.11

=1/3-1/4+1/4-1/5+1/5-1/6+...+1/9-1/10+1/10-1/11

=1/3-1/11

=8/33

Answer 2

1/12+1/20+1/30+...+1/90+1/110

=1/3.4+1/4.5+1/5.6+...+1/9.10+1/10.11

=1/3-1/4+1/4-1/5+1/5-1/6+...+1/9-1/10+1/10-1/11

=1/3-1/11

=8/33