Approximation and Simplification Questions for SBI PO

BODMAS Rule

BODMAS tells you the order to solve any expression: Brackets first, then Orders (powers and roots), then Division and Multiplication (left to right), then Addition and Subtraction (left to right). Violating this order is the single biggest source of errors in simplification questions. Think of it as traffic rules — everyone must follow the same sequence or there is a crash.

• B — Brackets: solve innermost bracket first, then curved, then square, then curly
• O — Orders: powers, square roots, cube roots
• DM — Division and Multiplication: treat as equal priority, solve left to right
• AS — Addition and Subtraction: treat as equal priority, solve left to right
• Never add before you multiply — classic SBI PO trap
• When nested brackets appear, work from inside out

Approximation Technique

In approximation questions, exact calculation is not needed — you round numbers to the nearest convenient value and then compute. The art is in deciding HOW MUCH to round. SBI PO options are usually spaced 50 to 200 apart, so rounding to the nearest 5 or 10 is safe. If you round too aggressively (nearest 100), two options may look equal. Round to nearest 5 as a default rule.

• Round to nearest 5 for safety; nearest 10 only if options are far apart
• For square roots: memorize squares up to 30 and cubes up to 15
• For percentages: convert to simple fractions (12.5% = 1/8, 37.5% = 3/8)
• Always round one number up and one down to cancel out rounding error
• If question has a sqrt of a messy number, find the two perfect squares it lies between
• Check: your approximated answer should be within 2-3% of actual to safely match an option

Key Fraction to Percentage Conversions

SBI PO approximation questions frequently hide percentages as decimals or fractions. Knowing these by heart saves 10-15 seconds per question — which adds up to 1-2 extra questions solved. Treat this table like a multiplication table: non-negotiable memorization.

• 1/6 = 16.67%, 1/7 = 14.28%, 1/8 = 12.5%, 1/9 = 11.11%, 1/11 = 9.09%, 1/12 = 8.33%
• 33.33% = 1/3, 66.67% = 2/3, 37.5% = 3/8, 62.5% = 5/8
• Use fraction form for multiplication — 12.5% of 640 = 640/8 = 80 (instant)
• Memorize squares: 1 to 30, and cubes: 1 to 15
• Memorize sqrt of 2 = 1.414, sqrt of 3 = 1.732, sqrt of 5 = 2.236

Surds and Indices Shortcuts

Simplification questions in SBI PO often include expressions with powers and roots. Knowing a few index laws cold lets you collapse complex expressions in seconds. The most tested patterns are: same base different powers, power of a power, and negative exponents.

• a^m x a^n = a^(m+n); a^m / a^n = a^(m-n)
• (a^m)^n = a^(mn); (ab)^n = a^n x b^n
• a^0 = 1 always; a^(-n) = 1/a^n
• a^(1/n) = nth root of a; a^(m/n) = (nth root of a)^m
• If bases are different, try to make them same — e.g., 8 = 2^3, 27 = 3^3
• For surds: rationalize denominator by multiplying numerator and denominator by conjugate

• Applying addition before multiplication — always check BODMAS before starting, even for simple-looking expressions
• Rounding both numbers in a division upward — this inflates the numerator and deflates denominator effect, giving a wrong answer; balance rounding direction
• Approximating square root of 625 as 24 or 26 instead of 25 — always verify neighbouring perfect squares before estimating
• Ignoring negative signs when using index laws — especially a^(-n) being treated as -a^n
• Spending more than 45 seconds on one approximation question — if stuck, use elimination from options and move on; these are speed questions not concept questions

• BODMAS = Big Orange Dogs Make Amazing Sandwiches — Brackets, Orders, Division, Multiplication, Addition, Subtraction
• For fractions: 1 PIZZA cut into equal slices — 1/8 slice is 12.5%, 1/4 slice is 25%, easy to visualize portion
• Surds shortcut: ROOT then POWER — always do the root first (a^(m/n) means root n first, then power m)
• Rounding balance rule: UP one DOWN one — if you round the first number up, round the second number down to keep the error small

• SBI PO Prelims typically has 5 approximation questions in a dedicated set — they appear together, so once your eye is trained, you enter a rhythm and finish all 5 in under 3 minutes
• SBI PO uses messier decimals than IBPS (e.g., 3.987 instead of 4.0) to test if you still round correctly — always check how far apart the options are before deciding rounding precision
• Simplification questions sometimes appear inside Data Interpretation as calculation steps — BODMAS errors there cascade into wrong DI answers, double damage
• If two options are very close (say 223 and 227), do NOT approximate aggressively — spend 10 extra seconds for accuracy; this is a deliberate SBI PO trap
• Practice target: 30 seconds per approximation question, 45 seconds per simplification question — time yourself on PYQs from 2019, 2022, and 2023 SBI PO papers which had the highest frequency of this topic