Question

A bacteria culture starts with 160 bacteria and grows at a rate proportional to its size. After 5 hours there will be 800 bacteria.

(a) Express the population after t hours as a function of t. population:_______________ (function of t)
(b) What will be the population after 7 hours? ____________
(c) How long will it take for the population to reach 2790? ______________

Answer 1

Explanation:

Let the rate at which the bacteria grow be represented by the exponential equation

P(t) = P0e^kt

P(t) is the population of the bacteria after time t

P0 is the initial population

k is the constant of variation

t is the time

If the initial Population is 160 bacteria's, them the equation becomes;

P(t) = 160e^kt

b) if After 5 hours there will be 800 bacteria, this means

at t = 5 p(t) = 800

Substitute and get k

800 = 160e^5k

800/160 = e^5k

5 = e^5k

Apply ln to both sides

Ln5 = lne^5k

ln5 = 5k

k = ln5/5

k = 0.3219

Next is to calculate the population after 7hrs i.e at t = 7

P(7) = 160e^0.3219(7)

P(7) = 160e^2.2532

P(7) = 160(9.5181)

P(7) = 1522.9

Hence the population after 7houra will be approximately 1523populations

c) To calculate the time it will take the population to reach 2790

When p(t) = 2790, t = ?

2790 = 160e^0.3219t

2790/160 = e^0.3219t

17.4375 = e^0.3219t

ln17.4375 = lne^0.3219t

2.8587 = 0.3219t

t = 2.8587/0.3219

t = 8.88 hrs

Hence it will take approximately 9hrs for the population to reach 2790