Number series – “×4 then subtract 1, 2, 3, 4, 5, …”: 8, 31, 122, 485, 1936, 7739, ? Continue the rule to obtain the next term.
Verbal Reasoning
Number Series
Difficulty: Medium
Choose an option
Answer
Correct Answer: 30950
Explanation
Introduction / Context:This pattern couples a strong multiplication (×4) with a steadily growing subtraction (−1, −2, −3, …). Such “multiply then adjust” constructions are frequently used to test multi-step pattern recognition under time pressure.
Given Data / Assumptions:
- 8 → 31 = 8*4 − 1
- 31 → 122 = 31*4 − 2
- 122 → 485 = 122*4 − 3
- 485 → 1936 = 485*4 − 4
- 1936 → 7739 = 1936*4 − 5
Concept / Approach:Next step uses −6 after ×4.
Step-by-Step Solution:
7739*4 = 30956.Subtract 6: 30956 − 6 = 30950.Verification / Alternative check:Each subtraction increment increases by 1, and the ×4 factor is constant across steps—both conditions satisfied.
Why Other Options Are Wrong:
46430, 34650, 42850 correspond to different adjustments and break the −6 continuation.Common Pitfalls:Assuming pure ×4; always check for small additive/subtractive ladders layered on a big multiplier.
Final Answer:30950