1/48+1/80+1/120+1/168

1/48+1/80+1/120+1/168
=1/(6*8)+1/(8*10)+1/(10*12)+1/(12*14)
=1/6-1/8+1/8-1/10+1/10-1/12+1/12-1/14
=1/6-1/14
=2/21

1/48=1/2*(1/6-1/8)
1/80=1/2*(1/8-1/10)
1/120=1/2(1/10-1/12)
1/168=1/2(1/12-1/14)

1/48+1/80+1/120+1/168
=1/2 *(1/6-1/14)
=1/2 *4/42
=2/42
=1/21

1/48+1/80+1/120+1/168
=（1/2）[（1/6-1/8）+（1/8-1/10）+（1/10-1/12）+（1/12-1/14）]
=（1/2）[1/6-1/14]
=（1/2）（7-3）/14
=1/7

=1/48+3/240+2/240+1/168
=1/48+5/240+1/168
=1/48+1/48+1/168
=1/24+1/168
=21/504+3/504
=1/21