Number series – fill in the missing term. Sequence: 15, __, 27, 27, 39, 39, …

Introduction / Context:
Many reasoning sequences repeat each term twice. Detecting this duplication pattern quickly reveals the missing entry. Here we test that recognition skill.

Given Data / Assumptions:

• Sequence begins: 15, __, 27, 27, 39, 39, …
• After the blank, the pattern clearly shows 27 repeated twice, and 39 repeated twice.
• Assume the same two-in-a-row behavior applies to the first value as well.

Concept / Approach:

Check for immediate repetition. If terms 3–4 and 5–6 are identical pairs (27, 27) and (39, 39), then terms 1–2 should also form (15, 15). Thus the blank is simply a copy of the preceding number.

Step-by-Step Solution:

Verification / Alternative check:

The sequence follows a “repeat twice” template: a, a, b, b, c, c, … . Plugging in 15 for the blank yields (15, 15, 27, 27, 39, 39), which perfectly fits the observed pattern.

Why Other Options Are Wrong:

39 and 51 would break the starter pair duplication. 23 introduces an arbitrary value with no supporting rule. The simplest, most consistent explanation is direct repetition.

Common Pitfalls:

Overcomplicating with unnecessary arithmetic progressions or ratios. First scan for simple structures like duplication before testing complex rules.

Final Answer:

15