Which of the following fraction is the largest ?

Answer: Option A

$$\begin{array}{rl}& \text{L}\text{.C}\text{.M}\text{.}\text{of}8,16,40\text{and}80=80\\ & \frac{7}{8}=\frac{70}{80};\frac{13}{16}=\frac{65}{80};\frac{31}{40}=\frac{62}{80}\\ & \text{Since},\frac{70}{80}>\frac{65}{80}>\frac{63}{80}>\frac{62}{80},\\ & \text{So},\frac{7}{8}>\frac{13}{16}>\frac{63}{80}>\frac{31}{40}\\ & \text{So},\frac{7}{8}\text{is}\text{the}\text{largest}\text{.}\end{array}$$