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Quantitative skills in economics

What you'll learn

  • How to calculate percentages, percentage changes, interest, averages, costs, revenue, profit and pay.
  • How to use PED, PES, GDP, CPI and current-account data in simple GCSE calculations.
  • How to construct and interpret supply and demand diagrams from data.
  • How to turn numbers into economic judgement, not just “do the maths”.

Why quantitative skills matter

In GCSE Economics, at least 10% of the total marks test quantitative skills. These are not meant to be scary: they are mostly Key Stage 3 maths used in economic contexts.

Definition

Economic data

Economic data means numerical information about the economy, such as prices, output, wages, inflation, unemployment, exports, imports or government spending.

The key habit is: calculate, interpret, then make a judgement. A number on its own is rarely enough.

Key Idea

Numbers need interpretation

A correct calculation tells you what has changed; good economics explains why it matters for consumers, producers, workers, government or the wider economy.

6.1 Percentages, percentage changes and interest

A percentage means “out of 100”. If a price rises by 5%, it rises by 5 for every 100 of the original price.

For percentage change, always compare the change with the original value.

Percentage change=new value−original valueoriginal value×100%\text{Percentage change} = \frac{\text{new value} - \text{original value}}{\text{original value}} \times 100\%Percentage change=original valuenew value−original value​×100%
Example

Calculating a percentage change

A meal deal rises from £3.50 to £4.00.

  1. Find the change: £4.00−£3.50=£0.50\text{£}4.00 - \text{£}3.50 = \text{£}0.50£4.00−£3.50=£0.50.
  2. Divide by the original value: £0.50£3.50≈0.143\frac{\text{£}0.50}{\text{£}3.50} \approx 0.143£3.50£0.50​≈0.143.
  3. Convert to a percentage: 0.143×100%≈14.3%0.143 \times 100\% \approx 14.3\%0.143×100%≈14.3%, so the price rose by about 14.3%.
Common Mistake

Wrong base in percentage change

Do not divide by the new value. Percentage change is based on the original value.

Interest on savings

Interest is the reward paid for saving money, usually shown as a percentage rate per year. When Bank of England base rates rose after the 2022–23 inflation spike, many savings accounts also paid higher interest.

Example

Calculating simple interest on savings

You save £2,000 in an account paying 3% interest per year.

  1. Convert 3% to a decimal: 0.03.
  2. Calculate the interest: £2,000×0.03=£60\text{£}2{,}000 \times 0.03 = \text{£}60£2,000×0.03=£60.
  3. Add it to the original savings if asked for the final amount: £2,000+£60=£2,060\text{£}2{,}000 + \text{£}60 = \text{£}2{,}060£2,000+£60=£2,060 after one year.

6.2 Totals, averages, costs, revenue and profit

A fixed cost is a cost that does not change with output in the short run, such as rent. A variable cost changes as output changes, such as ingredients or packaging.

Total cost is all costs added together. Total revenue is the money a firm receives from sales. Profit is what is left after costs are taken away from revenue.

Total revenue=price×quantity soldTotal cost=fixed cost+variable costProfit=total revenue−total cost\begin{aligned} \text{Total revenue} &= \text{price} \times \text{quantity sold} \\ \text{Total cost} &= \text{fixed cost} + \text{variable cost} \\ \text{Profit} &= \text{total revenue} - \text{total cost} \end{aligned}Total revenueTotal costProfit​=price×quantity sold=fixed cost+variable cost=total revenue−total cost​

An average is a total divided by the number of items. Average cost means cost per unit of output.

Average cost=total costoutput\text{Average cost} = \frac{\text{total cost}}{\text{output}}Average cost=outputtotal cost​
Example

Calculating revenue, costs, profit and average cost

A small bakery sells 500 pastries for £2 each. Fixed costs are £200. Variable cost is £0.80 per pastry.

  1. Calculate total variable cost: £0.80×500=£400\text{£}0.80 \times 500 = \text{£}400£0.80×500=£400.
  2. Calculate total cost: £200+£400=£600\text{£}200 + \text{£}400 = \text{£}600£200+£400=£600.
  3. Calculate total revenue: £2×500=£1,000\text{£}2 \times 500 = \text{£}1{,}000£2×500=£1,000.
  4. Calculate profit: £1,000−£600=£400\text{£}1{,}000 - \text{£}600 = \text{£}400£1,000−£600=£400 profit.
  5. Calculate average cost: £600500=£1.20\frac{\text{£}600}{500} = \text{£}1.20500£600​=£1.20 per pastry.

6.3 Income, gross pay and net pay

Income is money received, often from work, benefits, savings or profits.

Gross pay is pay before deductions. Net pay is pay after deductions such as income tax, National Insurance or pension contributions.

Net pay=gross pay−deductions\text{Net pay} = \text{gross pay} - \text{deductions}Net pay=gross pay−deductions
Example

Calculating gross and net pay

A part-time worker earns £11.50 per hour and works 20 hours. Deductions are £28.

  1. Calculate gross pay: £11.50×20=£230\text{£}11.50 \times 20 = \text{£}230£11.50×20=£230.
  2. Subtract deductions: £230−£28=£202\text{£}230 - \text{£}28 = \text{£}202£230−£28=£202.
  3. The worker’s net pay is £202.

Minimum-wage rises can increase workers’ gross pay, but they also raise labour costs for firms. That creates a trade-off between higher living standards for low-paid workers and higher costs for producers.

6.4 PED and PES

Price elasticity of demand, or PED, measures how responsive quantity demanded is to a change in price.

PED=percentage change in quantity demandedpercentage change in price\text{PED} = \frac{\text{percentage change in quantity demanded}}{\text{percentage change in price}}PED=percentage change in pricepercentage change in quantity demanded​

Price elasticity of supply, or PES, measures how responsive quantity supplied is to a change in price.

PES=percentage change in quantity suppliedpercentage change in price\text{PES} = \frac{\text{percentage change in quantity supplied}}{\text{percentage change in price}}PES=percentage change in pricepercentage change in quantity supplied​

If the answer is greater than 1, it is elastic. If it is less than 1, it is inelastic. Exactly 1 is unit elastic.

Example

Classifying PED and PES

  1. A supermarket raises the price of milk by 10%, and quantity demanded falls by 3%. PED is −3%10%=−0.3\frac{-3\%}{10\%} = -0.310%−3%​=−0.3. Using the size of the answer, 0.3 is less than 1, so demand is price inelastic.
  2. House prices rise by 8%, but the quantity of new homes supplied rises by only 2%. PES is 2%8%=0.25\frac{2\%}{8\%} = 0.258%2%​=0.25, so supply is price inelastic.
  3. This makes economic sense: essentials like milk often have inelastic demand, and housing supply can be slow to respond because building takes time and planning permission.
Tip

Elasticity shortcut

For PED, the answer is often negative because price and quantity demanded usually move in opposite directions. For GCSE classification, focus on the size of the number unless the question specifically asks about the sign.

6.5 Constructing and interpreting supply and demand graphs

Demand is the quantity consumers are willing and able to buy at different prices. Supply is the quantity producers are willing and able to sell at different prices.

The equilibrium price is where quantity demanded equals quantity supplied. A movement along a curve is caused by a change in price. A shift of a curve is caused by a non-price factor, such as income, tastes, production costs, taxes or technology.

The diagram below shows a rightward shift in demand, such as higher demand for streaming services during parts of the COVID-19 period.

Supply and demand diagram showing demand increasing from D1 to D2 and equilibrium rising from E1 to E2

At a price below equilibrium, quantity demanded is greater than quantity supplied: this is excess demand. At a price above equilibrium, quantity supplied is greater than quantity demanded: this is excess supply.

To show total revenue on a supply and demand diagram, draw a rectangle from the price level across to the quantity sold and down to the quantity axis. The area of the rectangle is:

Total revenue=price×quantity\text{Total revenue} = \text{price} \times \text{quantity}Total revenue=price×quantity
Example

Finding equilibrium and revenue from a schedule

Price per bottle (£)Quantity demandedQuantity supplied
210020
38040
46060
54080
  1. Find where quantity demanded equals quantity supplied: at £4, both are 60.
  2. So the equilibrium price is £4 and the equilibrium quantity is 60 bottles.
  3. At £3, quantity demanded is 80 and quantity supplied is 40, so excess demand is 40 bottles.
  4. Calculate total revenue at equilibrium: £4×60=£240\text{£}4 \times 60 = \text{£}240£4×60=£240.
Common Mistake

Shift or movement?

A change in the good’s own price causes a movement along the curve. A non-price factor causes the whole curve to shift.

6.6 GDP, real GDP and GDP per capita

Gross Domestic Product, or GDP, is the value of final goods and services produced in an economy over a period of time.

Nominal GDP uses current prices. Real GDP adjusts for inflation, so it is better for comparing output over time. GDP per capita means GDP per person.

GDP per capita=GDPpopulation\text{GDP per capita} = \frac{\text{GDP}}{\text{population}}GDP per capita=populationGDP​

If you are given a price index, you may use:

Real GDP=Nominal GDPprice index×100\text{Real GDP} = \frac{\text{Nominal GDP}}{\text{price index}} \times 100Real GDP=price indexNominal GDP​×100
Example

Calculating real GDP and GDP per capita

An economy has nominal GDP of £2,400 billion, a price index of 120, and a population of 67 million.

  1. Adjust GDP for inflation: (£2,400bn÷120)×100=£2,000bn\left(\text{£}2{,}400\text{bn} \div 120\right) \times 100 = \text{£}2{,}000\text{bn}(£2,400bn÷120)×100=£2,000bn real GDP.
  2. Divide real GDP by population: £2,000bn÷67m≈£29,850\text{£}2{,}000\text{bn} \div 67\text{m} \approx \text{£}29{,}850£2,000bn÷67m≈£29,850 per person.
  3. Interpret carefully: higher GDP per capita suggests higher average output per person, but it does not prove everyone is better off equally.

This matters when studying events like COVID-19, when UK output fell sharply and then recovered, while inflation later affected the meaning of “growth” in money terms.

6.7 CPI figures and inflation

The Consumer Prices Index, or CPI, measures the average price of a basket of goods and services bought by households.

Inflation is a sustained increase in the general price level. The inflation rate is the percentage change in CPI.

Inflation rate=new CPI−old CPIold CPI×100%\text{Inflation rate} = \frac{\text{new CPI} - \text{old CPI}}{\text{old CPI}} \times 100\%Inflation rate=old CPInew CPI−old CPI​×100%
Example

Calculating the inflation rate from CPI

CPI rises from 120 to 132.

  1. Find the change in CPI: 132−120=12132 - 120 = 12132−120=12 index points.
  2. Divide by the original CPI: 12120=0.10\frac{12}{120} = 0.1012012​=0.10.
  3. Convert to a percentage: 0.10×100%=10%0.10 \times 100\% = 10\%0.10×100%=10%, so the inflation rate is 10%.
Common Mistake

Inflation falling is not prices falling

If inflation falls from 10% to 4%, prices are usually still rising, just more slowly. Falling prices would be called deflation.

6.8 Current-account balance of payments figures

The current account records flows of money between the UK and the rest of the world for trade in goods and services, plus income flows. In simple GCSE questions, you may be given the figures needed to add and subtract.

A current-account surplus means more money flows in than out. A current-account deficit means more money flows out than in.

Current account balance=money in−money out\text{Current account balance} = \text{money in} - \text{money out}Current account balance=money in−money out
Example

Calculating a current-account balance

Suppose the UK has exports and income from abroad of £860 billion, and imports and income paid abroad of £920 billion.

  1. Identify money in: £860 billion.
  2. Identify money out: £920 billion.
  3. Calculate the balance: £860bn−£920bn=−£60bn\text{£}860\text{bn} - \text{£}920\text{bn} = -\text{£}60\text{bn}£860bn−£920bn=−£60bn.
  4. The negative answer means a current-account deficit of £60 billion.

Trade data can help evaluate issues such as Brexit, exchange-rate changes or energy imports, but data alone does not prove one single cause.

6.9 Using data to support economic decisions

Charts, graphs and tables help you justify decisions. When using data, look for:

  • the direction of change: rising, falling or stable
  • the size of change: small or large
  • comparisons: between years, firms, countries or groups
  • context: COVID-19, energy shocks, interest-rate changes, minimum-wage rises, taxes or regulation
  • judgement: who gains, who loses, and whether the evidence is enough
Example

Using data to justify a business decision

A café currently sells 1,000 coffees at £3 each. Energy costs rise by £200 per week. The café considers raising price to £3.30. Estimated PED is 0.5.

  1. A rise from £3 to £3.30 is a 10% price rise. With PED of 0.5, quantity demanded is expected to fall by 5%, so sales fall from 1,000 to 950 coffees.
  2. Calculate new revenue: £3.30×950=£3,135\text{£}3.30 \times 950 = \text{£}3{,}135£3.30×950=£3,135. Old revenue was £3×1,000=£3,000\text{£}3 \times 1{,}000 = \text{£}3{,}000£3×1,000=£3,000, so revenue rises by £135.
  3. Compare the result with the cost increase: extra revenue of £135 does not fully cover the £200 rise in energy costs, so the café may need another response as well.
  4. Evaluate ethically: raising prices may protect the business and jobs, but it may also make coffee less affordable for regular customers.
Exam technique

In the exam

  1. Write the formula, substitute the numbers, and keep the units: £, %, people, tonnes or index points.
  2. After calculating, add one sentence explaining what the answer means in context.
  3. For graphs, label axes, curves, equilibrium and shifts clearly; state whether there is excess demand, excess supply or a new equilibrium.
Self review

Check yourself

  • Can you explain why percentage change uses the original value?
  • Can you calculate profit, average cost and net pay from a short set of figures?
  • Can you identify equilibrium and excess demand from a supply and demand table or diagram?
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Quantitative skills in economics are mostly simple maths used in context. The key exam habit is calculate the number, interpret what it means, then make a judgement about who gains, who loses, or whether the change is large enough to matter.

Percentage change compares the change with the original value, not the new value. The following formula measures how big the change is relative to the starting point:

Percentage change=new value−original valueoriginal value×100% \text{Percentage change} = \frac{\text{new value} - \text{original value}}{\text{original value}} \times 100\% Percentage change=original valuenew value−original value​×100%

Simple interest is the amount saved multiplied by the annual rate in decimal form. If you save £2000 at 3%3\%3%, interest after one year is 2000×0.03=602000 \times 0.03 = 602000×0.03=60, so the balance becomes £2060.

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Quantitative skills in economics Revision Guide

  1. GCSE
  2. /Economics
  3. /Quantitative skills in economics