(1/4*1/7+1/7*1/10+1/10*1/13+1/13*1/16)*3
=1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16
=1/4-1/16
=3/16
=1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16
=1/4-1/16
=3/16
(1/4*1/7+1/7*1/10+1/10*1/13+1/13*1/16)*3
=(1/4-1/7)+(1/7-1/10)+(1/10-1/13)+(1/13-1/16)
=1/4-1/16
=3/16