Given: Average marks obtained by 8 students = 51 Average marks obtained by 9 students = 68 Calculation: Total marks obtained by 8 students =51×8 ⇒ 408 Total marks obtained by 9 students =68×9 ⇒ 612 The total marks obtained by 17 students =408+612 ⇒ 1020 Required average =1020/17 ⇒ 60 ∴ The average marks of all the students are 60.