The average of 24 observations is 41. The average of the first 9 observations is 42 and the average of the last 16 observations is 39. What is the value of the 9th observation?

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).