36×(1/2+1/3+1/6)

36x(1/2+1/3+1/6)=36x1/2+36x1/3+36x1/6=18+12+6=369/20x199+9/20 =9/20x(199+1) =9/20x200=90（1/4-1/7）x28 =1/4x28-1/7x28 =7-4=31/4x101-1/4=1/4x(101-1