Question

A culture started with 5,000 bacteria. After 2 hours, it grew to 6,500 bacteria. Predict how many bacteria will be present after 18 hours. Round your answer to the nearest whole number.

Answer 1

This can be expressed as exponential growth of the form:

f=ir^t, f=final amount, i=initial amount, r=common ratio (rate), t=time

In this case we are given the point (2, 6500) and i=5000 so we can solve for the rate...

6500=5000r^2  divide both sides by 5000

1.3=r^2  take the square root of both sides and note that we know r>0

r=1.3^(1/2) so our equation becomes:

f=5000(1.3)^(1/2)^t  and knowing that (a^b)^c=a^(b*c) we can say:

f=5000(1.3)^(t/2)  so for t=18

f=5000(1.3)^9

f≈53022  (to nearest whole bacteria)