In a History examination, the average for the entire class was 80 marks. If 10% of the students scored 95 marks and 20% scored 90 marks, what was the average marks of the remaining students of the class ?

Answer: Option C

Let the number of students in the class be 100 and let the required average be $$x$$
Then,
⇒ (10 × 95) + (20 × 90) + (70 × $$x$$) = (100 × 80)
⇒ 70$$x$$ = 8000 - (950 + 1800)
⇒ 70$$x$$ = 5250
⇒ $$x$$ = 75