Introduction
Number series and mental ability questions appear in almost every Bangladeshi government job examination — BCS (preliminary), Bank (Senior/Assistant Officer), and especially IT-officer and computer operator posts. In a number-series question you are shown a sequence of numbers that follow a hidden rule (pattern), and you must find the missing term or the next term. Mental-ability questions extend this idea to letters, analogies, coding-decoding, odd-one-out and simple logical reasoning.
Why it matters: these questions are pure logic — no syllabus to memorise. Once you learn the standard pattern families and a fast diagnostic method, you can score full marks in seconds. Because each question typically takes only 15–30 seconds, this is one of the highest return-per-minute areas of the whole exam. Speed here buys you time for harder quantitative problems.
Learning objectives
- Understand what a number series is and how a "pattern rule" defines it.
- Recognise the main families: arithmetic, geometric, difference, mixed/alternating, square/cube, prime, Fibonacci-type and interpolated series.
- Apply a step-by-step diagnostic procedure to identify any pattern quickly.
- Solve letter series and alphanumeric series using letter-position numbering.
- Handle mental-ability items: analogies, coding-decoding, odd-one-out.
- Avoid the classic traps (single vs. double pattern, sign errors, direction of change).
- Manage exam time and self-check answers.