GATE CS 2015 Set 1 QGA-6 — General Aptitude

The number of students in a class who have answered correctly, wrongly, or not attempted each question in an exam, are listed in the table below. The marks for each question are also listed. There is no negative or partial marking.$$\begin{array}{|c|c|c|c|c|} \hline \textbf{Q No.} & \textbf{Marks} &\textbf{Answered}&\textbf{Answered}&\textbf{Not}\\&&\textbf{ Correctly} &\textbf{Wrongly} & \textbf{Attempted} \\ \hline \text{1} & \text{2} &\text{21} &\text{17} &\text{6}\\ \hline \text{2} & \text{3} &\text{15} & \text{27}& \text{2}\\ \hline \text{3} & \text{1} &\text{11} & \text{29} & \text{4}\\ \hline \text{4} & \text{2} &\text{23} & \text{18} & \text{3}\\ \hline \text{5} & \text{5} &\text{31} & \text{12} & \text{1} \\ \hline \end{array}$$What is the average of the marks obtained by the class in the examination?