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