The number of students in a class who have answered correctly, incorrectly, or not attempted each question in an examination is shown in the table below. The marks for each question are also listed. There is no negative or partial marking.

Q. No	Marks	Answered correctly	Answered incorrectly	Not Attempted
1	1	20	10	10
2	2	15	15	10
3	5	20	20	0
4	10	12	15	13

Find the average of the marks obtained by the class in the examination