Discrete vs Continuous Math Example 2

Follow the full solution, then compare it with the other examples linked below.

Example 2

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A discrete model counts bacteria in a culture as B(t)=2tB(t) = 2^t (where tt is in hours, integer values). A continuous model uses B(t)=e0.693tB(t) = e^{0.693t}. Compare the models at t=0,1,2,3t = 0, 1, 2, 3 and explain when each is appropriate.

Solution

  1. 1
    Discrete (2t2^t): t=0:1t=0: 1, t=1:2t=1: 2, t=2:4t=2: 4, t=3:8t=3: 8.
  2. 2
    Continuous (e0.693te^{0.693t}, noting lnโก2โ‰ˆ0.693\ln 2 \approx 0.693): e0=1e^0 = 1, e0.693โ‰ˆ2e^{0.693} \approx 2, e1.386โ‰ˆ4e^{1.386} \approx 4, e2.079โ‰ˆ8e^{2.079} \approx 8.
  3. 3
    At integer times the models agree. The continuous model also gives values between integers (e.g., at t=1.5t=1.5: e1.04โ‰ˆ2.83e^{1.04} \approx 2.83), whereas bacteria truly exist only in whole numbers.
  4. 4
    Discrete is more accurate for small populations; continuous is convenient for calculus-based analysis and large populations.

Answer

Both give 1,2,4,81, 2, 4, 8 at t=0,1,2,3t = 0,1,2,3. Discrete is exact for integer counts; continuous is useful for large populations and mathematical analysis.
Real phenomena are often inherently discrete (individual bacteria, people, photons), but continuous models using exponentials and calculus are easier to analyse mathematically. For large enough quantities, the continuous approximation is excellent.

About Discrete vs Continuous

The distinction between quantities that take separate, distinct values (discrete, like number of students) and quantities that can take any value in a range (continuous, like height or temperature).

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