Arithmetic — Percentage, Profit & Loss, Interest — IBPS PO Quant
Arithmetic word problems are the language the rest of bank quant speaks. Directly they're 5–8 marks a paper; indirectly they're inside almost every caselet, every DI comparison and every mixture question. And they all run on one toolkit: convert percentages to fractions, use the multiplying factor to reach the final value in one step, and know how simple and compound interest relate. Master that, and percentage, profit-loss, discount and interest stop being separate chapters and become one set of templates.
1. What IBPS actually asks
Directly: 5–8 questions split across percentage, profit-loss-discount, simple & compound interest, and partnership, plus their appearance inside caselet DI. The bank flavour leans on relationships ("SP is 20% above CP, a 10% discount is given…") and clean numbers engineered for the fraction route.
2. The percentage core (everything builds on this)
, and the single biggest speed unlock is converting percentages to fractions before calculating: 12.5% = ⅛, 16.67% = ⅙, 37.5% = ⅜, 62.5% = ⅝.
The multiplying factor (MF): every percentage change is one multiplication.
- +20% → ×1.20 (or ×6/5); −25% → ×0.75 (or ×3/4). Never compute "the change" and add it back — go straight to the final value.
Successive change: two changes then net to (signs matter). +20% then −20% = −4%, never zero.
3. Profit, loss & discount (percentage on prices)
All of it is percentage applied to Cost Price (CP), Selling Price (SP), Marked Price (MP):
- Profit% ; Loss% on CP likewise. The base is always CP for profit/loss.
- SP from CP: — the multiplying factor again.
- Discount is on MP: .
- The MP–CP chain: goods marked above cost, then discount ⇒ net profit% (same successive-change formula).
Key traps: profit% is on CP but discount% is on MP — never mix bases. And "20% profit" as a fraction is 1/5 of CP, so CP : SP = 5 : 6; ratio thinking beats formula-plugging.
4. Simple vs compound interest (interest = percentage over time)
- SI is linear: the same interest every year. CI compounds: interest on interest.
- The gap for 2 years: — a one-line result IBPS asks constantly. For 3 years, .
- CI as growth: compound interest is population-growth math — is the same multiplying factor chained times.
- Half-yearly compounding: rate → , time → .
Ratio shortcut: at , the CI amounts over years form a GP with ratio ; and SI makes equal yearly additions — spotting which one applies saves the whole calculation.
5. Partnership (ratio of capital × time)
Profit is shared in the ratio of each partner's capital × months invested:
If A invests ₹12,000 for 12 months and B ₹18,000 for 8 months, ratio . "Working vs sleeping partner" and salary-before-split are just adjustments on top of this ratio.
6. The templates IBPS reuses
- Consumption–price: price + with fixed spend ⇒ consumption −. (25% up ⇒ 20% down.)
- % more ↔ % less: A is more than B ⇒ B is less than A. Convert to a fraction and flip.
- Two successive discounts: then = single equivalent discount.
- Exam/marks and mixtures reuse the same percentage-gap logic.
Solved examples
Q1 (profit as ratio). A article is sold at a 25% profit for ₹500. The cost price is?
Show explanation
Solution. 25% profit ⇒ CP:SP = 4:5. SP = ₹500 ⇒ CP = 500 × 4/5 = ₹400.
Q2 (marked-up then discounted). Goods marked 40% above cost are sold at a 25% discount. Net profit%?
Show explanation
Solution. Net = 40 − 25 − (40×25)/100 = 15 − 10 = +5%.
Q3 (CI − SI, 2 years). The difference between CI and SI on ₹8,000 at 10% for 2 years is?
Show explanation
Solution. ₹80.
Q4 (successive discount). Two successive discounts of 20% and 10% equal a single discount of?
Show explanation
Solution. 20 + 10 − (20×10)/100 = 30 − 2 = 28%.
Q5 (partnership). A puts ₹15,000 for 8 months, B ₹12,000 for 10 months. B's share of ₹9,600 profit?
Show explanation
Solution. Ratio = 15×8 : 12×10 = 120 : 120 = 1:1 ⇒ B gets ₹4,800.
Q6 (consumption–price). Sugar price rises 25%; by what % must a family cut use to keep spend unchanged?
Show explanation
Solution. 20% (25% = ¼ up ⇒ ⅕ down).
8. The protocol
For every arithmetic question:
- Convert every percentage to a fraction as you read.
- Identify the base — CP for profit/loss, MP for discount, principal for interest.
- Reach for the multiplying factor to jump to the final value in one step.
- Match to a template (successive change, % more/less, consumption–price, CI−SI, partnership ratio).
- Use ratios over formulas when the percentage is a clean fraction (25% ⇒ 4:5).
- If the arithmetic turns ugly, you picked the wrong base — re-read "per cent of what".
