Approximation Questions for SBI PO

What is Approximation

Approximation means replacing awkward numbers (decimals, square roots, cube roots, fractions) with nearby round numbers that are easier to work with. You then do quick arithmetic and pick the answer option closest to your result. The key insight: you do NOT need the exact answer. You just need to be closer to one option than the others. SBI PO keeps the options spread far enough apart that rounding to the nearest 10 or even 50 is usually sufficient.

• Round each number to the nearest convenient value before operating.
• Never waste time doing long division or exact multiplication.
• Answer choices in SBI PO are typically spaced 20-100 units apart — so a rough answer is enough.
• Always check: are you rounding UP or DOWN? Consistent rounding in one direction can skew your answer.
• If two options are very close, do one more step of refinement — but this is rare in SBI PO.

Rounding Strategy — Do It in One Pass

The best technique is a left-to-right one-pass approach. Look at the full expression, round every number in one glance, then compute. Do not round, compute partially, then re-read the question. That wastes 20-30 seconds per question. Treat the expression like a mini assembly line: scan and replace all numbers, then calculate once.

• Numbers ending in 1, 2 round down. Numbers ending in 7, 8, 9 round up. 5, 6 round up.
• For numbers like 3498, round to 3500. For 4213, round to 4200.
• Decimals like 0.49 treat as 0.5, decimals like 67.3 treat as 67.
• sqrt(624): nearest perfect square is 625 = 25 squared, so sqrt(624) ≈ 25.
• Cube roots: cbrt(215) ≈ 6 because 6 cubed = 216. Memorise cubes 1-15.
• For percentages: 33.2% ≈ 33%, 66.8% ≈ 67% — do not over-think.

Must-Memorise Values for SBI PO

Certain values appear repeatedly in bank exam approximation questions. If these are stored in memory, you skip calculation entirely. Think of this as your cheat sheet burned into your brain.

• Squares: 1 to 30 must be known cold. 31 to 40 are good to know.
• Cubes: 1 cubed to 15 cubed — especially 11=1331, 12=1728, 13=2197, 14=2744, 15=3375.
• Square roots of non-perfect squares: sqrt(2)=1.41, sqrt(3)=1.73, sqrt(5)=2.23, sqrt(6)=2.45, sqrt(7)=2.65.
• Common fractions: 1/3=0.33, 2/3=0.67, 3/8=0.375, 5/8=0.625, 7/8=0.875.
• Powers of 2 up to 2 to the power 10 = 1024. Useful in compound interest and data interpretation combos.
• Percentage-fraction equivalents: 12.5%=1/8, 16.67%=1/6, 37.5%=3/8, 62.5%=5/8, 87.5%=7/8.

Error Compensation Technique

When you round one number up, try to balance by rounding another number in the same expression down, if both contribute in the same direction (both additions or both multiplied). This keeps your answer close to the true value. However, do NOT spend time doing this for every question — only use it when two options are within 30 of each other, which is rare in SBI PO Prelims.

• If you round 498 up to 500 (+2), and the next number is 203, round it down to 200 (-3) to roughly balance.
• In multiplication, if you round one factor up by 2%, try rounding the other factor down by 2%.
• In subtraction, rounding both numbers up by similar amounts is safe — errors cancel.
• This technique is a backup, not a routine step. Speed over precision in SBI PO.

• Rounding a number like 6995 to 6000 instead of 7000 — always look at the correct digit position before rounding.
• Computing sqrt(500) as 20 instead of ~22.4 — memorise that sqrt(484)=22 and sqrt(529)=23, so sqrt(500) is about 22.3, not 20.
• Rounding both numbers in a division DOWN — for example 398/19.8 rounded to 400/20=20, which is fine, but rounding to 380/18 inflates the answer. Keep division consistent: round both up or both down.
• Spending 60+ seconds trying to get an exact answer when the 5 options are spread 100 units apart — pure time waste in a speed test.
• Ignoring operator signs — students sometimes add when they should subtract after rounding. Read the sign AFTER rounding, not before.

• SCAN-REPLACE-COMPUTE: Three-word drill. Scan the expression, Replace numbers with round values, Compute once. Never revisit.
• The 5-UP Rule: Any digit 5 or above after your cut point rounds UP. Below 5 rounds DOWN. Five goes up, like a 5-star hotel is always upgraded.
• SQCUBE Board: Visualise a 2-column board in your mind — left column perfect squares (1,4,9...900), right column perfect cubes (1,8,27...3375). Before every exam, run through it once mentally.
• Fraction-Percent Twins: 12.5 and 1/8 are twins, 16.67 and 1/6 are twins, 37.5 and 3/8 are twins. Pair them up and remember as family units.

• SBI PO Prelims almost always has exactly 5 approximation questions grouped together. Target all 5 in 2.5 to 3 minutes — that is 30-36 seconds per question.
• Recent SBI PO papers (2022-2024) have increased use of cube roots and mixed operations (percentage + square root in same expression) to slow down students — drill these combos specifically.
• The wrong answer traps are often the result you get if you forget to apply an operation or misread a sign — always recheck the operator after rounding.
• SBI PO occasionally embeds approximation inside Data Interpretation questions as a calculation shortcut — the skill transfers directly, so it has double value.
• If you are stuck between two close options, check whether your rounding was uniformly upward or downward and adjust slightly — but cap this thinking at 10 seconds and move on.