20 QUESTIONS · 5 TOPICS · EULER'S METHOD EXPLORER · ABOUT 15 MINUTES

Nature doesn't give you the answer. It gives you the rate of change.

Populations, cooling coffee, swinging pendulums and spreading viruses all follow rules about how fast things change. Differential equations turn those rules into predictions. Twenty questions, each explained, then step a solution forward yourself. No sign-up, nothing saved.

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Population growthMalthus, 1798dP/dt = kP
CoolingNewton, 1701dT/dt = −k(T − Tₐ)
Spring / pendulumHooke, 1678x″ = −ω²x
Radioactive decayRutherford, 1900dN/dt = −λN
QUESTION 1 / 20 · BASICSEasy

What is the order of y″ + 3y′ − y = 0?

EULER'S METHOD

Step forward one slope at a time

When an equation can't be solved by hand, computers step along it: read the slope, walk a little way, repeat. Bigger steps are faster but drift from the true curve. Pick a model and change the step size.

exact solutionEuler steps
EXPONENTIAL GROWTHdy/dt = 0.8y, y(0) = 1Growth proportional to size. Euler always undershoots here, because the slope keeps rising during each step.
14.76Euler's estimate at the end
24.53exact value
Error 9.77 (40%).Over 10% off: each step follows a slope that's already out of date.

What this differential equations test covers, in short

Twenty multiple-choice questions on ordinary differential equations at first- to second-year university level, four on each of five topics: basics, first-order methods, second-order linear equations, modelling, and numerical methods.

You'll need comfortable calculus; try the calculus test first if you're rusty. The test is our own and not normed.

By What's Your IQ · Reviewed 5 Oct 2026
Format
20 multiple-choice questions
Level
First- to second-year university
Bonus
Euler's method explorer, 3 models
Scope
Ordinary (not partial) differential equations

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