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MicroeconomicsWorked example
Price rises from $10 to $12 and quantity demanded falls from 100 to 80. Is demand elastic?
%ΔQ = −20%
%ΔP = +20%
PED = −20 / 20 = −1
Unit elastic: total revenue stays the same.
Open the AP Microeconomics guideMacroeconomicsWorked example
The MPC is 0.8 and government spending rises by $50bn. How far can GDP rise?
multiplier = 1 / (1 − 0.8) = 5
ΔGDP = 5 × 50 = 250
Up to $250bn, before any crowding out.
Open the AP Macroeconomics guideStatisticsWorked example
Scores are normal with mean 70 and SD 10. What share scored above 85?
z = (85 − 70) / 10 = 1.5
P(Z > 1.5) = 1 − 0.933
About 6.7% scored above 85.
Open the AP Statistics guideMicroeconomicsWorked example
Income rises 10% and demand for bus travel falls 5%. What is YED?
YED = −5% / 10% = −0.5
Negative YED: bus travel is an inferior good.
Open the Cambridge 9708 hubMacroeconomicsWorked example
Nominal GDP is $550bn and the GDP deflator is 110. What is real GDP?
real GDP = 550 / 110 × 100
Real GDP is $500bn.
Open the Macroeconomics guideEconometricsWorked example
You omit ability, which raises wages and is positively correlated with schooling. Which way is the schooling coefficient biased?
bias = β₂ × corr(S, A)
(+) × (+) = (+)
Upward: the return to schooling is overstated.
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Every topic in syllabus order, with worked examples and practice questions.
DEconomicsMicro and macro: demand and supply, elasticity, market structures, GDP, inflation, money and policy.GuidesBlogBooksCase studies
σStatisticsDescribing data, probability, the normal distribution, hypothesis tests and regression.GuidesBlogBooks
∂MathematicsCalculus and optimisation for economists, functions, and first and second order conditions.BlogBooks soon
βEconometricsOLS, omitted variable bias, heteroskedasticity, instrumental variables and dummy variables.BlogBooks soon
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Development economics
Why some countries grow and others stay poor, how inequality and human development are measured, and what war does to an economy. Every article uses real data with full references.
20 country case studiesThe Economics of WarUkraine, Gaza, Sudan, Syria, Yemen, Lebanon, Iraq, Korea, post-war Germany and Japan, and more: output, inflation, debt, trade and recovery, indicator by indicator.Read the series →
Measuring developmentHuman Development IndexThe formula, a worked calculation and the latest rankings.
InequalityLorenz curve and Gini coefficientHow to calculate and read inequality, with World Bank data.
Growth modelsThe Harrod–Domar modelSavings, the capital-output ratio and the financing gap.
Growth modelsThe Solow growth modelSteady state, the golden rule and convergence.
Structural changeThe Lewis dual-sector modelSurplus labour and the turning point.
Trade and developmentComparative advantageOpportunity cost, terms of trade and worked examples.
Step-by-step guides
Start at step 1 and work through. Plain language, worked examples and practice at every step.
Microeconomics28 steps, from scarcity to market failure
- The economic problem
- The production possibility curve
- Comparative advantage
- Demand
Macroeconomics23 steps, from GDP to the open economy
- Gross domestic product
- Unemployment
- Inflation and price indices
- The business cycle
Statistics22 steps, from describing data to regression
- Statistical thinking
- Data and how it’s collected
- Describing data with graphs
- Describing data with numbers
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Case studies: economics in the real world
Examiners reward real examples. 100 cases, each with a data table, the economics explained, a worked calculation and an exam-style question.
The UK sugar taxElasticity and Pigouvian taxes
Zimbabwe’s hyperinflationMV = PQ and dollarisation
Google’s search monopolyNetwork effects and antitrust
OPECCartels and the prisoner’s dilemma
UK austerity 2010–19Fiscal multipliers
Bangladesh’s garment industryComparative advantage
Buy the 100 case studies for $9Usually $15. Also included in the Economics and Complete bundles.
New book · The Economics of War
What does war do to an economy?
Output collapses, prices soar, debt piles up and people leave. Then, sometimes, a remarkable recovery. Twenty case studies, told with real data from the IMF, the World Bank and the UN.
- 20case studies
- 430pages
- 100+charts
- 750+sources cited
Ukraine−28.8%real GDP in 2022, the year of the full-scale invasionRead the case study →Sudan−23.5%real GDP in 2023, then −19.3% in 2024 (IMF)Read the case study →Yemen−58%GDP per person since 2015 (World Bank)Read the case study →Syria$67.5bn → $21.4bnGDP in current dollars, 2011 to 2024Read the case study →Lebanon$51.6bn → $20.1bnGDP in current dollars, 2019 to 2023Read the case study →Strait of Hormuz20m barrelsof oil a day passed through the strait in 2024, a fifth of world useRead the case study →Iraq−36.7% → +53.4%real GDP in 2003, then the rebound in 2004Read the case study →Kuwait+82.8%real GDP growth in 1992, after falls of 26.2% and 41.0%Read the case study →Bosnia−75%GDP per person during the 1992–95 war (World Bank)Read the case study →Afghanistan45% of GDPcame from aid in 2018–2020, before it stoppedRead the case study →Germany and Japan−64%German GDP per person, 1944 to 1946, before the “miracle”Read the case study →Ethiopia9.8% a yearaverage growth in 2010–2019, before the Tigray warRead the case study →
All 20 case studies in one bookCharts, timelines, exam-style questions with answer guides and full references. Instant PDF download.
Most-read guides
- Z-Scores and the Normal Distribution: A Plain-English GuideStatistics
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- Heteroskedasticity: What It Is, Why It Matters, and How to Fix ItEconometrics
- Profit Maximisation with Calculus: First and Second Order ConditionsMathematics
Free formula sheetsMicroeconomics, macroeconomics and statistics: every formula your exam can ask, one page each, plus z, t, χ² and F tables.Open the formula sheets
Open the book before you buy it
Each chapter explains the idea in plain words, works through a diagram and the numbers, then ends with exam questions and a mark scheme.
Textbook chapter
Price elasticity of demand
Elasticity measures how strongly buyers react when the price changes. When demand is elastic, a small price rise loses a large share of sales.
\(PED = \dfrac{\%\Delta Q_d}{\%\Delta P}\)
Worked examplePrice rises 10%, quantity falls 25%. PED = −2.5: demand is elastic, so revenue falls.
Exam practice
A cinema cuts ticket prices from $12 to $9 and weekly sales rise from 2,000 to 3,000. Calculate PED and explain what happens to revenue. [4 marks]
| %ΔQ = +50%, %ΔP = −25% | 1 |
| PED = −2 | 1 |
| Demand is price elastic | 1 |
| Revenue rises from $24k to $27k | 1 |