Two interleaved sequences: fill the last two terms. Series: 20, 20, 19, 16, 17, 13, 14, 11, ?, ? Identify the odd/even position patterns and compute the missing pair.

Split into two subsequences

• Odd positions: 20, 19, 17, 14, ?, ? → differences: −1, −2, −3, −4, −5 ⇒ next terms: 14 − 4 = 10, then 10 − 5 = 5
• Even positions: 20, 16, 13, 11, ?, ? → differences: −4, −3, −2, −1, 0 ⇒ next terms: 11 − 1 = 10, then 10 − 0 = 10

Assemble the sequence … 14, 11, 10, 10

Note The question asks for the last two terms (positions 9 and 10), which are 10 and 10.