Interleaved Sequences
Two completely independent sequences are merged into one by alternating their terms.
Interleaved Sequences are a favourite in PiCompany Connector assessments and appear regularly in SHL Verify G+ tests too. The key insight: the sequence has two sub-sequences hidden inside it — one formed by terms at odd positions (1st, 3rd, 5th…) and another by terms at even positions (2nd, 4th, 6th…). Once you split them out, each half is usually a simple arithmetic or geometric sequence. Longer sequences with 7 or more terms are a strong signal to check for this pattern first.
How to solve it
- 1Write the terms on two separate lines: odd-position terms on line 1, even-position terms on line 2.
- 2Check whether each line now forms a simple arithmetic or geometric sequence.
- 3If yes: identify the rule for each sub-sequence, then extend whichever one contains the missing term.
- 4A sawtooth shape (high, low, high, low) is almost always an Interleaved pattern.
- 5The two sub-sequences often move in opposite directions (one goes up, the other goes down).
Worked examples
Example 1
Arithmetic and descending
Rule: Odd positions: +1 · Even positions: −10
Example 2
Two geometric sequences
Rule: Odd positions: ×2 · Even positions: ×3
Example 3
Multiply and halve
Rule: Odd positions: ×2 · Even positions: ÷2
Common mistakes
- Computing differences between all consecutive terms without splitting first. The differences will look random.
- Confusing this with Alternating Operator. Here the two halves are completely independent sequences, not two operations applied to one sequence.
- Forgetting to identify which position the missing term is in before applying the rule. An odd-position answer needs the odd-position rule.
Ready to practice?
Work through timed Interleaved Sequences questions and track your accuracy.