Find the missing term: 20, 20, 19, 16, 17, 13, 14, 11, ?, ?

Let the missing terms of the series be x₁ and x₂.
Thus, the sequence 20, 20, 19, 16, 17, 13, 14, 11. x₁, x₂ is a combination of two series:
I. 20, 19, 17, 14, x₁ and
II. 20, 16, 13, 11, x₂
The pattern in I is - 1, - 2, - 3,..............So, missing term, x₁= 14 - 4 = 10
The pattern in II is - 4, - 3, - 2,.......... So,missing term, x₂ = 11 - 1 = 10