The 20-Minute Battle in Bank Prelims
In Bank PO examinations (SBI PO, IBPS PO, RRB Scale I), you are given only 20 minutes to solve 35 quantitative questions. That leaves roughly 34 seconds per question!
Traditional school methods will run you out of time. To score 28+ marks in Quant, you must master rapid mental calculations that turn multi-step multiplications into 3-second mental operations.
Trick 1: Base 100 Multiplication Method
Multiply numbers close to 100 within seconds:
Example: Multiply $96 \times 94$
- Difference from 100: $96$ is $-4$, and $94$ is $-6$.
- Cross subtract: $96 - 6 = 90$ (or $94 - 4 = 90$).
- Multiply the differences: $(-4) \times (-6) = 24$.
- Put them together: 9024!
Example: Multiply $107 \times 108$
- Difference from 100: $+7$ and $+8$.
- Cross add: $107 + 8 = 115$.
- Multiply differences: $7 \times 8 = 56$.
- Answer: 11556!
Trick 2: Squaring Any Number Ending in 5
For any number ending in 5:
- Multiply the tens digit $(n)$ with its successor $(n+1)$.
- Append $25$ at the end.
- $65^2 = (6 \times 7) \text{ & } 25 = 4225$
- $85^2 = (8 \times 9) \text{ & } 25 = 7225$
- $115^2 = (11 \times 12) \text{ & } 25 = 13225$
Trick 3: Solving Quadratic Equations by Sign Method
In Banking exams, 5 questions on Quadratic Equations ($ax^2 + bx + c = 0$ and $py^2 + qy + r = 0$) appear regularly. Instead of applying factorisation formulas, memorize the Root Sign Table:
| Equation Signs ($b, c$) | Roots Sign ($x_1, x_2$) |
| :---: | :---: |
| $+ , +$ | $- , -$ |
| $- , +$ | $+ , +$ |
| $+ , -$ | $- , +$ |
| $- , -$ | $+ , -$ |
Golden Shortcut:
If in both equations the constant terms ($c$ and $r$) are negative (i.e. $- , -$), then Relationship Cannot be Established (CND) is the answer 100% of the time, without doing any calculations!
Trick 4: Fast Percentage Calculation by Splitting
Never calculate percentages mechanically. Break them into friendly benchmarks ($50\%, 10\%, 5\%, 1\%$).
Calculate $36\%$ of $450$:
- $36\% = 50\% - 10\% - 4\%$
- Alternatively: $36\% \times 450 = 450\% \times 36$
- $400\% \text{ of } 36 = 144$
- $50\% \text{ of } 36 = 18$
- Total = $144 + 18 = 162$!
Applying these rules routinely during daily practice will give you an insurmountable speed advantage in SBI and IBPS preliminary exams.
