Difficulty: Easy
Correct Answer: 23 25
Explanation:
Introduction / Context:
This is a classic two-interleaved-arithmetic-series problem frequently seen in reasoning tests. One subsequence is increasing while the other is decreasing. We must identify the pattern and then supply the next two terms.
Given Data / Assumptions:
Concept / Approach:
Split the sequence by odd and even positions (1-indexed): the odd-position terms form one arithmetic progression; the even-position terms form another. Then compute each trend independently.
Step-by-Step Solution:
Odd positions: 1st=17, 3rd=19, 5th=21, 7th=23 → each step +2. So the 9th term should be 25.Even positions: 2nd=32, 4th=29, 6th=26 → each step −3. So the 8th term should be 23.Therefore, the next two terms (8th and 9th) are 23 and 25 respectively.
Verification / Alternative check:
Write the two progressions explicitly: even-index series 32, 29, 26, 23 (−3 each time) and odd-index series 17, 19, 21, 23, 25 (+2 each time). Merging them preserves the given order.
Why Other Options Are Wrong:
Common Pitfalls:
Looking for a single-step rule across all numbers rather than separating into interleaved subsequences often obscures the simple arithmetic patterns.
Final Answer:
23 25
Discussion & Comments