Approximation and Rounding-Off Techniques
Approximation and Rounding-Off Techniques
Approximation questions look intimidating — decimals like 23.97, 449.02 and 15.98% scattered through a long expression — but they are among the easiest marks in the entire paper. The secret is to stop solving exactly and start rounding smartly. In SBI Clerk you are never asked for the precise value; you are asked for the option closest to it, and that changes everything about how you should work.
The One Rule: Round to Convenient Numbers
Replace every messy number with the nearest whole number or an easy fraction, compute the simple expression, and pick the closest option. Because the five options in a bank paper are spread far apart, small rounding errors almost never push you to the wrong choice. The mental shift required is to trust the approximation and resist the urge to 'be accurate' — accuracy here just wastes time you cannot spare.
| Given | Round to | Why it is safe |
|---|---|---|
| 449.02 | 450 | nearest 10, tiny error |
| 23.97 | 24 | nearest whole number |
| 15.98% | 16% | clean percentage |
| 1/6.98 | 1/7 | clean known fraction |
| √624 | 25 (√625) | nearest perfect square |
Shortcut: Approximate Percentages as Fractions
Convert awkward percentages into fractions you already know: 16.66% ≈ 1/6, 12.5% ≈ 1/8, 33.33% ≈ 1/3 and 14.28% ≈ 1/7. A question like '16.66% of 4998' then becomes 1/6 × 5000 = 833 in a single step, with no multiplication of decimals at all. This one habit turns the scariest-looking approximation sums into the fastest.
Answer ≈ (rounded numbers combined) → choose the nearest option
Solved Examples
Example 1: 449.02 + 23.97 × 3.02. Round to 449 + 24 × 3 = 449 + 72 = 521, then pick the option nearest 521. Notice you never touched a decimal point.
Example 2: 39.98% of 649.87. Round to 40% of 650 = 0.4 × 650 = 260. Here 40% is even cleaner as 2/5, giving 2/5 × 650 = 260 the same way.
Example 3: (15.02)² − (8.97)². Round to 15² − 9² = 225 − 81 = 144. Recognising the near perfect squares is what makes this instant.
✗ Solving 449.02 + 23.97 × 3.02 exactly with decimal multiplication | ✓ Round to 449 + 72 = 521 and pick the nearest option
How Much Rounding Is Safe
A fair worry is that rounding might change the answer, so build a simple sense of margin. If your two nearest options differ by, say, 40 or more, then rounding each number to the nearest whole is completely safe. If two options sit unusually close — within 5 or 10 of each other — round more gently, to one decimal place instead of a whole number, and the closest option still stands out clearly. In SBI Clerk the options are almost always widely spaced, so aggressive rounding is the right default and you only tighten up on the rare closely-spaced set.
सन्निकटन में सटीक उत्तर नहीं, सबसे नज़दीकी विकल्प चाहिए। हर संख्या को नज़दीकी पूर्णांक या जानी-पहचानी भिन्न में बदलें और तेज़ी से हल करें।
Exam Pointer — Expect about 5 approximation questions in SBI Clerk Prelims, and they are gift marks worth roughly 15 seconds each. The one genuine trap is rounding both terms in the same direction on a subtraction, which magnifies the error — when subtracting, round the larger term down and the smaller term up so the gap stays honest.
60-Second Recap
- Never solve exactly — round to whole numbers or easy fractions.
- Memorise percentage-to-fraction pairs (16.66% = 1/6, 12.5% = 1/8).
- Options are far apart, so smart rounding is always safe.
- 5 easy marks at about 15 seconds each — clear these first.