解1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)=1+(1/2-1/2)+(1/3-1/3)+(1/4-1/4)-1/5=1-1/5=4/5
60分之163
