Question

Suppose the bacteria population in a specimen increases at a rate proportional to the population at each moment. There were 100 bacteria 4 days ago and 100,000 bacteria 2 days ago. How many bacteria will there be by tomorrow

Answer 1

9514 1404 393

Answer:

  about 3,160,000,000

Step-by-step explanation:

"Increases at a rate proportional to population" means the growth is exponential. It can be modeled by the equation ...

  p = ab^t

We can find 'a' and 'b' using the given data points.

  100 = ab^(-4) . . . . . . . population 4 days ago

  100,000 = ab^(-2) . . . population 2 days ago

Dividing the second equation by the first, we find ...

  1000 = b^2

  b = 1000^(1/2)

Substituting for b in the first equation, we have ...

  100 = a(1000^(1/2))^(-4) = a(1000^-2)

  100,000,000 = a

Then the population model is ...

  p = 100,000,000×1000^(t/2)

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Tomorrow (t=1), the population will be ...

  p = 100,000,000 × 1000^(1/2) ≈ 31.6 × 100,000,000

  p ≈ 3,160,000,000 . . . . . bacteria by tomorrow

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Additional comment

We could write this as ...

  p = 10^(8+1.5t)

Then for t=1, this is p = 10^(8+1.5) = 10^0.5 × 10^9 = 3.16×10^9