Simplification and Approximation Questions for IBPS RRB PO

BODMAS Rule — The Foundation

Every simplification question follows a fixed order of operations. BODMAS stands for Brackets, Orders (powers/roots), Division, Multiplication, Addition, Subtraction. You must strictly follow this sequence or you will get wrong answers even if your arithmetic is correct. Think of BODMAS as a traffic signal — you cannot jump a step.

• Solve innermost brackets first: (), then {}, then []
• Orders means squares, cubes, square roots — solve these before multiply/divide
• Division and Multiplication are equal priority — solve left to right
• Addition and Subtraction are equal priority — solve left to right
• Never add before you multiply — the most common mistake
• In RRB PO, most simplification questions test 2-3 BODMAS steps combined

Key Arithmetic Identities to Memorise

RRB PO simplification questions heavily use algebraic identities hidden inside big expressions. Recognising these saves 30-40 seconds per question. If you see a² - b², immediately factor it. These are not fancy — they are shortcuts the examiner deliberately puts to reward prepared students.

• (a+b)² = a² + 2ab + b²
• (a-b)² = a² - 2ab + b²
• a² - b² = (a+b)(a-b) — most frequently tested identity
• (a+b)³ = a³ + 3a²b + 3ab² + b³
• a³ + b³ = (a+b)(a² - ab + b²)
• a³ - b³ = (a-b)(a² + ab + b²)

Fraction and Decimal Shortcuts

A large chunk of RRB PO simplification involves messy fractions and decimals. The fastest approach is to memorise fraction-to-percentage equivalents and use them to estimate or simplify. Also, learn to convert repeating decimals to fractions quickly.

• 1/8 = 0.125, 1/6 = 0.1667, 1/7 = 0.1428, 3/8 = 0.375, 5/8 = 0.625
• When adding fractions, find LCM of denominators first — never cross-multiply for 3+ fractions
• 0.999... = 1 (recurring decimal shortcut — useful in approximation)
• To multiply decimals: ignore decimals, multiply integers, then place decimal point
• Dividing by 0.5 is same as multiplying by 2; dividing by 0.25 is multiplying by 4

Approximation Technique — Round and Attack

Approximation questions give you a messy expression and 5 answer options that differ by noticeable amounts (like 120, 140, 160, 180, 200). You do NOT need exact calculation — round numbers to nearest comfortable value and compute fast. The skill is knowing how much to round without overshooting the answer band.

• Round to nearest 5 or 10 depending on how close answer choices are
• If choices are far apart (differ by 20+), aggressive rounding is safe
• If choices are close (differ by 5-10), round more carefully or do one exact step
• Always round square roots to nearest whole number: √143 ≈ 12, √224 ≈ 15
• Percentage approximation: 33.3% ≈ 1/3, 66.7% ≈ 2/3, 12.5% = 1/8
• Cube roots: memorise cubes up to 15³ = 3375 for fast recognition

Squares, Cubes, and Roots — Must Memorise Table

RRB PO setters love hiding perfect squares and cubes inside expressions. If you do not have these memorised, you waste 30-60 seconds recognising them. Think of this table as your lookup database — no exam strategy replaces memorisation here.

• Squares: 1² to 30² must be on fingertips (especially 12 to 25)
• Cubes: 1³=1, 2³=8, 3³=27, 4³=64, 5³=125, 6³=216, 7³=343, 8³=512, 9³=729, 10³=1000, 12³=1728, 15³=3375
• Square roots of non-perfect squares: √2=1.414, √3=1.732, √5=2.236, √6=2.449, √7=2.646
• Recognise: 1024=2¹⁰=32², 729=27²=3⁶, 2401=7⁴=49²
• Cube root trick: last digit of cube determines last digit of cube root (e.g., cube ending in 3 → cube root ends in 7)

• Ignoring BODMAS and solving left to right blindly — example: 2 + 3 × 4 is 14 not 20
• In approximation, rounding both numbers in the same direction (both up or both down) when they are being subtracted — this doubles the error instead of cancelling it
• Confusing 0.abab (repeating) with 0.ab (terminating) — using wrong denominator in fraction conversion
• Not simplifying surds before computing — attempting to multiply 3√12 × 2√3 without first simplifying √12 = 2√3
• Spending more than 60 seconds on one simplification question — in RRB PO prelims, if a question takes over 90 seconds, skip and return; the section has enough easy ones

• BODMAS = Big Orange Dogs Must Always Sit — Brackets, Orders, Division, Multiplication, Addition, Subtraction
• Fraction friends: 1/8 family — 1/8=0.125, 3/8=0.375, 5/8=0.625, 7/8=0.875. Notice they all end in 5.
• Cube root last digit map: 1→1, 2→8, 3→7, 4→4, 5→5, 6→6, 7→3, 8→2, 9→9, 0→0. Pairs to remember: 2-8 and 3-7 swap each other.
• For approximation, think of it as archery — you do not need a bullseye, just land in the scoring zone. Round boldly when options are spread wide.

• IBPS RRB PO Prelims 2023 and 2022 had 10 simplification and 5 approximation questions — together they form 37-40% of the Quant section, making this the single highest-weight topic
• Simplification in RRB PO is slightly easier than IBPS PO — expect 2-3 step BODMAS questions, not 5-step ones. Target all 10 within 8 minutes.
• Approximation questions in RRB PO tend to use square roots and percentages together — practice the combo: sqrt(something close to perfect square) × percentage of round number
• Do not use a column method for these questions. Mental math with rounding is the intended approach. Pencil work should be minimal — just intermediate numbers.
• If you see a question with variable x or y labelled as a simplification, it may be a quadratic disguised. Do not panic — factorize and solve like algebra, not pure arithmetic.