Posted by **amelia** on Tuesday, December 15, 2009 at 7:55am.

I'm not sure how to do this question

7. The growth of bacteria in culture can be described by the equation

N1 = N0e'

where N is the number of bactena at any time t, No is the initial number of bacteria, and k

is a constant. The time taken for growth to double the number of bacteria of a particular

strain (the 'doubling time') was 30 mm. A culture was started with 200 bacteria of this

strain

Determine the followmg (giving appropnate units in each case)

(a) the value of k for this strain (2]

(b) the rate of increase m bacterial number when the number in the colony

was 2000 131

(c) the minimum number of bacteria in this culture (1]

for a i calculated k =0.023 or (ln 2)/30

for c i think it would be at t = 0

Nt = No.e^(k0)

Nt = No.e^0

Nt = No.1

Nt = No = 200

i don't know how to do b and im not sure if im right with a and c please help

- Math -
**drwls**, Tuesday, December 15, 2009 at 8:50am
I cannot follow what you are doing. Your original equation

N1 = N0e'

is wrong, and you quote a doubling time im millimeters.

To obtain help, you need to be more careful posting your questions.

- Math -
**Reiny**, Tuesday, December 15, 2009 at 8:55am
First of all your opening equation should have been

N1 = N0 e^(kt), where t is in minutes.

Does 30 mm mean "30 minutes" ? (I assumed that)

I did get the same value of k.

so your equation is

N = 200 e^(.023105t)

the rate of increase is the derivative of your function, so

dN/dt = 200(.023105) e^(.023105t)

So we now have to find the value of t when N = 2000131

2000131 = 200 e^(.023105t)

for that I got t = 398.6 minutes

(you better check my arithmetic here)

Now sub that t value back into our derivative to find the rate of change at that time.

c) is a strange question. Since it is exponential growth, the minimum value would be at the start, namely 200

- Math -
**amelia**, Tuesday, December 15, 2009 at 9:03am
sorry it was a copy and paste job should checked it thanks for the help

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