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This bilingual Number Series item asks the learner to solve “Solve this Number Series question: Study the number series 51, 45, 39, 33, 27, ?.
The verified answer to “Solve this Number Series question: Study the number series 51, 45, 39, 33, 27, ?. Why option A is right: 21 preserves the constant difference of -6 throughout the series. This working identifies the relevant number pattern and connects the given information to the required result. A plausible-looking option is not sufficient unless it reproduces the complete number pattern.
FAQ
Common questions and clear answers for this topic.
21, option C.
Rebuild and verify the complete number pattern.
30, 24, 27 break a clue, direction, transition or operation.
Replay the rule from the first clue or term and test every intermediate step.
Number Series questions present a sequence of numbers following a specific pattern, and the candidate must identify the pattern to find the missing or wrong number. Common types: Arithmetic series (constant difference), Geometric series (constant ratio), Square/cube series, Prime number series, Fibonacci series, and Alternating series. Number Series is frequently asked in SSC CGL, IBPS Bank PO, RRB NTPC, and SBI Clerk exams.
An Arithmetic Progression (AP) is a number series where the difference between consecutive terms is constant (common difference d). Example: 2, 5, 8, 11, 14 (d=3) or 20, 16, 12, 8 (d=-4). Formula: nth term = a + (n-1)d where a is first term. To identify AP, subtract consecutive terms - if the difference is constant, it is an AP. These are the easiest number series questions in competitive exams.
