Numbers a, b, c, d, e and f are such that the average of a, b and c is 21; that of c, d and e is 31; that of e and f is 14 and that of c and e is 14. Find the average of a, b, c, d, e and f.

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).