Average marks obtained by 80 students in an examination is 50 = 80X50 = 4000 Is average of both passed and failed students that is 80 students total marks

failed students are 30 as per question.

If failed students are 30, then 80-30= 50 students (passed)

50 passed students average is 55 which means 50×55 =2750

total average is 4000 and passed students average is 2750

remaining students average (failed students ) = 1250

failed students average is 1250 which as to be divided by 30 students