Question

1/3+1/6+1/10+1/15+1/21+```````+1/105+1/120

Answer 1

1/3+1/6+1/10+1/15+1/21+```````+1/105+1/120

=1/2(1/2-1/3+1/3-1/4+…………+1/15-1/16)

=1/2(1/2-1/16)

=7/32