Question

3/1×5+3/5×9+3/9×13+……+3/55×59

Answer 1

1/1×5=(1-1/5)/4

1/5×9=(1/5-1/9)/4

...

1/55×59=(1/55-1/59)/4

原式=3*(1-1/5+1/5-1/9+...+1/55-1/59）/4

=3*(1-1/59）/4

=87/118