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

The average of 100 numbers is 40. If one of the numbers, 30, is replaced by 70 while keeping the other numbers same, what is the new average?

The arithmetic mean of 22.5, 56, 42.5, 2x + 1, x - 2, 3x, and 36 is 30. Find the value of x (where x > 0).