Elasticity: Demand & Supply – Types, Factors, Applications

TAKEAWAYS:

• Elasticity measures how much quantity changes when price or income changes—not the same as slope.
• Price elasticity of demand (PED) tells if demand is elastic, inelastic, or unitary; supply elasticity does the same for producers.
• Total revenue test is a shortcut to check elasticity without calculations.
• Factors affecting elasticity (substitutes, necessities vs luxuries, time period) explain why some goods have high/low elasticity.
• Cross-elasticity and income elasticity help analyze market behavior beyond just price changes.
• NEB exam focus: Graphs, numerical problems, and real-world applications (e.g., petrol vs salt) are key.

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What is Elasticity?

Elasticity is a measure of how responsive quantity demanded or supplied is to changes in price, income, or prices of related goods. Unlike slope (which is absolute), elasticity is relative—it tells us percentage change, not just units.

Why is Elasticity Important?

• Helps businesses set prices (e.g., should a shop raise prices if demand is inelastic?).
• Guides governments on tax policies (e.g., taxing elastic goods reduces revenue).
• Explains market trends (e.g., why petrol prices rise but demand stays high).

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1. Price Elasticity of Demand (PED)

Definition: PED measures how much quantity demanded changes when the price of a good changes, keeping other factors constant.

Formula: $$\text{PED}=\frac{\%\text{ change in quantity demanded}}{\%\text{ change in price}}$$ Or (using midpoint formula for accuracy): $$\text{PED}=\frac{\Delta Q/(Q_1+Q_2)/2}{\Delta P/(P_1+P_2)/2}$$

Types of PED

How to Remember?

• Elastic (>1): Demand is sensitive to price (e.g., if price of iPhones rises, many switch to Android).
• Inelastic (<1): Demand doesn’t change much (e.g., petrol—people still buy even if prices rise).
• Unitary (=1): % change in Qd = % change in P (e.g., some fast-moving consumer goods).

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2. Determinants of PED

Factors that make demand more or less elastic:

Example:

• Salt: Inelastic (no substitutes, necessity).
• Holidays: Elastic (many alternatives, luxury).

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3. Total Revenue Test (Shortcut to Find PED)

Instead of calculating PED, you can use total revenue (TR) to guess elasticity:

• If price ↑ and TR ↑ → Demand is inelastic (e.g., petrol).
• If price ↑ and TR ↓ → Demand is elastic (e.g., luxury watches).
• If price ↑ and TR unchanged → Unitary elastic.

Worked Example: A shop sells 100 pens at ₹10 each (TR = ₹1000).

• If price rises to ₹15, sales drop to 80 pens (TR = ₹1200). → TR increased → Inelastic demand (PED < 1).
• If price rises to ₹12, sales drop to 50 pens (TR = ₹600). → TR decreased → Elastic demand (PED > 1).

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4. Price Elasticity of Supply (PES)

Definition: PES measures how much quantity supplied changes when the price of a good changes.

Formula: $$\text{PES}=\frac{\%\text{ change in quantity supplied}}{\%\text{ change in price}}$$

Types of PES

Determinants of PES

Example:

• Wheat: Elastic in long run (farms can expand), inelastic in short run (fixed land).
• Concert tickets: Inelastic (limited seats).

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5. Cross Elasticity of Demand (XED)

Definition: Measures how quantity demanded of Good A changes when the price of Good B changes.

Formula: $$\text{XED}=\frac{\%\text{ change in Qd of Good A}}{\%\text{ change in price of Good B}}$$

Types of XED

Worked Example:

• If price of coffee ↑, demand for tea ↑ → Substitutes (XED > 0).
• If price of petrol ↑, demand for cars ↓ → Complements (XED < 0).

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6. Income Elasticity of Demand (YED)

Definition: Measures how quantity demanded changes when consumer income changes.

Formula: $$\text{YED}=\frac{\%\text{ change in Qd}}{\%\text{ change in income}}$$

Types of YED

Worked Example:

• If income ↑ and demand for luxury cars ↑ → YED > 1 (Luxury good).
• If income ↑ and demand for buses ↓ → Inferior good (YED < 0).

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7. Applications of Elasticity

For Businesses

• Pricing strategies: Charge high prices for inelastic goods (e.g., medicine).
• Promotions: Discounts work best for elastic goods (e.g., electronics).
• Product differentiation: If substitutes exist, firms must innovate to reduce elasticity.

For Governments

• Taxation: Tax inelastic goods (e.g., petrol) to raise revenue without reducing demand much.
• Subsidies: Give subsidies on necessities (e.g., food) to help poor people.
• Price controls: Inelastic goods (e.g., medicine) should not have price ceilings (shortages may occur).

Real-World Example: COVID-19 Lockdown

• Demand for masks: Inelastic (necessity) → Prices rose but demand stayed high.
• Demand for holidays: Elastic (luxury) → Many cancelled trips when prices rose.

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8. Common Mistakes to Avoid

1. Confusing elasticity with slope:

   • Elasticity is about percentage change, not just units.
   • A steep demand curve can be elastic if % changes are large.

2. Ignoring time period:

   • Demand for petrol is inelastic in the short run but may become elastic in the long run (people switch to electric cars).

3. Mixing PED and PES:

   • Demand elasticity is about buyers, supply elasticity is about sellers.

4. Assuming all necessities are inelastic:

   • Some necessities (e.g., organic food) can be elastic if substitutes exist.

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Exam Tip: How to Score Full Marks in NEB Questions

NEB exams test concepts, calculations, and applications. Here’s how to ace Unit 6:

1. Numerical Problems (3-5 Marks)

• Always use the midpoint formula to avoid mistakes.
• Show all steps (e.g., % change calculations).
• Interpret the answer (e.g., "Since PED = 0.5, demand is inelastic...").

NEB-Style Question: "If the price of a good rises from ₹50 to ₹60 and quantity demanded falls from 100 to 80 units, calculate PED and state whether demand is elastic or inelastic."

Solution:

1. Calculate % change in Qd: $$\frac{80-100}{(80+100)/2}\times 100=\frac{-20}{90}\times 100=-22.22\%$$
2. Calculate % change in P: $$\frac{60-50}{(60+50)/2}\times 100=\frac{10}{55}\times 100=18.18\%$$
3. PED = $\frac{-22.22}{18.18}=-1.22$ (Ignore negative sign for elasticity).
4. Since PED > 1, demand is elastic.

2. Graph-Based Questions (4-6 Marks)

• Label axes clearly (e.g., "Price (₹)" on Y-axis, "Quantity (units)" on X-axis).
• Draw curves correctly:
  • Elastic: Flatter slope.
  • Inelastic: Steeper slope.
• Show shifts vs movements:
  • Price change → Movement along the curve.
  • Income/preferences change → Shift of the curve.

NEB-Style Question: "Draw a demand curve for an elastic good. If price rises from ₹20 to ₹30, show the change in quantity demanded and total revenue."

Solution:

• Explanation:
  • Initial TR = ₹20 × Q1.
  • New TR = ₹30 × Q2 (but Q2 drops more than proportionally).
  • TR falls → Confirms elasticity.

3. Short Answer Questions (2-3 Marks)

• Define key terms (e.g., "PED is the responsiveness of quantity demanded to a change in price...").
• Give real examples (e.g., "Salt has inelastic demand because...").
• Compare concepts (e.g., "Difference between PED and YED").

NEB-Style Question: "Distinguish between elastic and inelastic demand with examples."

Solution:

4. Application-Based Questions (5-7 Marks)

• Relate theory to real life (e.g., "How does elasticity affect tax policies?").
• Use local examples (e.g., "Why is demand for electricity inelastic in Nepal?").

NEB-Style Question: "Why does the Nepal government impose high taxes on cigarettes but not on salt? Use the concept of elasticity."

Solution:

1. Cigarettes:

   • Elastic demand (many substitutes like gutka, betel leaf).
   • High taxes reduce consumption (people quit or switch).
   • Revenue increases because demand is sensitive to price.

2. Salt:

   • Inelastic demand (necessity, no close substitutes).
   • High taxes do not reduce demand much → less revenue.
   • People cannot easily avoid salt.

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Final Revision Checklist

✅ Memorize formulas (PED, PES, XED, YED). ✅ Know the 5 determinants of PED and PES. ✅ Practice graph drawing (elastic vs inelastic curves). ✅ Solve 5-10 numerical problems (use midpoint formula). ✅ Relate to Nepal’s economy (e.g., petrol, electricity, agriculture).

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Good luck! Elasticity is all about how much buyers and sellers react—master this, and you’ll ace the NEB exam. 🚀