In SSC CGL, you rarely need to solve a question fully — you just need to eliminate wrong options fast. These 5 short tricks let you do exactly that, without writing a single full calculation.
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1. Unit Digit Method
Look only at the last digit of the numbers involved. Multiply/add just the unit digits and match it against the unit digits of the given options — wrong options get eliminated instantly.
| Question | Unit Digit Logic | Result |
|---|---|---|
| 347 × 263 = ? | Unit digits: 7 × 3 = 21 | Answer ends in 1 |
| 23⁴ = ? | 3, 9, 7, 1 (cycle of 4) → 3⁴ ends in | Answer ends in 1 |
2. Last Two Digits Method
Same idea as Unit Digit, taken one step further. Calculate only the last two digits of the result (equivalent to finding the remainder on division by 100). Useful when multiple options share the same unit digit.
| Question | Last Two Digit Logic | Result |
|---|---|---|
| 786 × 354 = ? | 86 × 54 → last two digits = 24 | Answer ends in 24 |
| 123 × 127 = ? | 23 × 27 = 621 → last two digits = 21 | Answer ends in 21 |
3. Decimal Values Method
For division, root, or fraction-based questions, count expected decimal places instead of computing the full value. The number of digits after the decimal in the options is often enough to eliminate 2–3 choices.
| Question | Decimal Logic | Result |
|---|---|---|
| √50 ≈ ? | √49 = 7, √64 = 8 → value lies just above 7 | ≈ 7.07 |
| 22 ÷ 7 = ? | 22/7 is a known approximation | ≈ 3.14 |
4. Divisibility and Multiples Method
Apply standard divisibility rules directly on the options to rule out values that can't possibly be correct.
| Divisor | Rule |
|---|---|
| 2 | Last digit is 0, 2, 4, 6, or 8 (even numbers) |
| 3 | Sum of digits divisible by 3 |
| 4 | Last two digits divisible by 4 |
| 5 | Last digit is 0 or 5 |
| 6 | Divisible by both 2 and 3 |
| 7 | Double the last digit and subtract it from the rest of the number, result is divisible by 7 |
| 8 | Last three digits form a number divisible by 8, |
| 9 | Sum of digits divisible by 9 |
| 10 | Last digit is 0 |
| 11 | (Sum of odd-place digits) − (sum of even-place digits) divisible by 11 |
| 12 | Divisible by both 3 and 4 |
5. Digital Sum Method
Add up the digits of a number repeatedly until a single digit remains — this is the digital sum. The digital sum of an answer must match the digital sum derived from the question, making it a fast way to verify options.
| Question | Digital Sum Logic | Result |
|---|---|---|
| 123 + 456 = ? | DS(123)=6, DS(456)=6 → 6+6=12 → DS=3 | Answer's DS must be 3 |
| 48 × 36 = ? | DS(48)=3, DS(36)=9 → 3×9=27 → DS=9 | Answer's DS must be 9 |
Note: Digital Sum is primarily a verification tool — use it to cross-check an answer you've already shortlisted, not as a standalone method.
Quick Reference
- Unit Digit: Use for multiplication/power-based options with different unit digits.
- Last Two Digits: Use when unit digits match but options still differ.
- Decimal Values: Use for roots, divisions, and fraction comparisons.
- Divisibility & Multiples: Use when options are whole numbers tied to a known factor.
- Digital Sum: Use as a final check after narrowing down to 1–2 options.
Pro Topper Tip
Combine two tricks together — for example, eliminate options using Unit Digit first, then confirm with Digital Sum. This combo alone can save 15–20 seconds per question.