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Worksheets›Calculus›Differential equations›Exponential growth and decay models (dy/dt = ky)

Exponential Growth and Decay Models (dy/dt = Ky) Worksheets

Free printable worksheets with answer keys. Pick a level, preview the questions, then open the sheet to swap or delete any single question.

CalculusAnswer key includedPDF · Print
Open in generatorStart with an easy sheet

Easy: Predicting growth

  1. 1.dydt = 0.06y, y(0) = 60y(10) ≈
  2. 2.dydt = 0.1y, y(0) = 380y(2) ≈
  3. 3.dydt = 0.15y, y(0) = 360y(9) ≈
  4. 4.dydt = 0.15y, y(0) = 130y(10) ≈
  5. 5.dydt = 0.04y, y(0) = 470y(2) ≈
  6. 6.dydt = 0.05y, y(0) = 350y(2) ≈
Preview shows 6 of 12 questions. Every sheet is new; open it to change any question.

Worksheet variations

When a quantity changes at a rate proportional to its size, dy/dt = ky. Separating variables and integrating gives y = y₀e^(kt), where y₀ is the starting amount. k > 0 means growth and k < 0 decay. If the amount doubles in time T, then e^(kT) = 2, so k = ln 2 ÷ T.

Easydydt = 0.1y, y(0) = 380y(10) ≈ Predicting growthMediumdydt = −0.12y, y(0) = 150y(9) ≈ Predicting decayHardA population growing by dy/dt = ky doubles every 18 years. Find k.Finding k from a doubling time

How to solve it: a worked example

Use y = y₀e^(kt). Round to the nearest hundredth.

  1. Startdydt = 0.08y, y(0) = 410y(3) ≈
  2. The solution of dy/dt = kyy = 410e0.08t
  3. Substitute the timey(3) = 410e0.08 × 3 ≈ 521.21
  4. Answer≈ 521.21

Common mistakes to watch for

  • Using y₀ + kt (linear growth) instead of y₀e^(kt).
  • Giving k a positive sign for decay.
  • Using log base 10 instead of ln when solving for k.

Tip: tick “Step-by-step answer key” in the generator to print each step for marking.

Related worksheets

Differential equations: initial value problemsLimits by direct substitutionLimits by factoring (0/0 forms)Limits at infinityDerivatives with the power rule

FAQ

Why does dy/dt = ky give exponential growth?

It says the rate of growth is proportional to the current amount, so the more there is, the faster it grows. The function with that property is y = y₀e^(kt).

How do you find k from a doubling time?

Set y = 2y₀ at the doubling time T: 2 = e^(kT), so k = ln 2 / T. For a half-life, k = −ln 2 / T.

Is every worksheet different?

Yes. Numbers are generated each time, and the answer key is calculated for that sheet. Swap any single question and its answer updates too.

Can I mix exponential growth and decay models (dy/dt = ky) with other skills?

Yes. In the generator, add more skills; each gets its own section on the sheet with its own instructions.

Is it free to print?

Yes. Generating and printing from the browser is free with no sign-up. PDF downloads need a free account.