The average marks obtained by Sachin in five subjects is two more than his average marks in four subjects. If Sachin secured 66 marks in the fifth subject, find his average marks in the 5 subjects.

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).