Introduction
The subtopic Data & Numbers forms the quantitative backbone of the WBCS Preliminary and Main examinations. Within the broader syllabus of Quantitative Aptitude, this area tests your ability to recognise numerical patterns, apply fundamental arithmetic operations, manipulate exponents and surds, solve counting problems, handle date‑and‑calendar logic, and work with elementary set theory. In the last eight years (2016–2023), WBCS has asked 17 questions directly from this subtopic, covering a rich variety of sub‑themes: number sequences, composite numbers, exponential equations, digit counting, permutation and combination applications, perfect square constructions, calendar calculations, inequalities, and pattern matching with alphanumeric series.
The examiners are not looking for rote memorisation; they want you to think flexibly with numbers. Many questions are deceptively simple—like “what is the smallest composite number?”—yet a surprising number of aspirants trip because they confuse composite with prime. Others involve multi‑step reasoning, such as the 2020 problem where a cyclic sum condition forces you to deduce a specific term. The difficulty range is from straightforward (WBCS 2016, “how many days between two dates?”) to moderately tricky (WBCS 2020, exponential equation yielding three unknowns). No question requires calculus or advanced algebra; all are solvable with a solid grasp of middle‑school mathematics and careful logical application.
This chapter is designed to be your comprehensive reference. We will start from first principles—defining every jargon term before using it, building conceptual foundations, and then diving deep into the specific question types that have appeared. Along the way, we will embed every PYQ (Previous Year Question) from the 17 provided, explaining not only the correct answer but also why the distractors are plausible. By the end, you will have a framework for tackling any new Data & Numbers question that WBCS can throw at you, and you will be equipped with memory aids, pattern‑recognition techniques, and a clear sense of what might appear next.