The average of marks obtained by A and B is 15 less than that of average marks obtained by B and C. If the marks obtained by C is 65, What is the marks obtained by A?

$$\eqalign{ & {\text{According to the question,}} \cr & \left( {\frac{{B + C}}{2}} \right) - \left( {\frac{{A + B}}{2}} \right) = 15 \cr & \Rightarrow \frac{{B + C - A - B}}{2} = 15 \cr & \Rightarrow \frac{{C - A}}{2} = 15 \cr & \Rightarrow C - A = 30 \cr & C = 65 \cr & \therefore A = 35 \cr} $$