4/3-7/12+9/20-11/30+13/42-15/56=1/3(4-7/4)+1/10(9/2-11/3)+1/14(13/3-15/4)=1/3(4-7/4)+1/10(4+1/2-4+1/3)+1/14(4+1/3-4+1/4)=1/3*9/4+1/10*5/6+1/14*7/12=9/12+1/12+1/24=21/24=7/8
