Answer:
339
Step-by-step explanation:
Exponential Function
General form of an exponential function: [tex]y=ab^x[/tex]
where:
If b > 1 then it is an increasing function
If 0 < b < 1 then it is a decreasing function
Given information:
Therefore: [tex]y=240b^x[/tex]
To find an expression for the population after 1 hour, substitute x = 1 into the found equation:
[tex]\implies y=240b^1[/tex]
[tex]\implies y=240b[/tex]
We are told that the population after 9 hours is double the population after 1 hour. Therefore, make y equal to twice the found expression for the population after 1 hour, let x = 9, then solve for b:
[tex]\implies 2(240b)=240b^9[/tex]
[tex]\implies 480b=240b^9[/tex]
[tex]\implies 480=240b^8[/tex]
[tex]\implies 2=b^8[/tex]
[tex]\implies b=\sqrt[8]{2}[/tex]
[tex]\implies b=2^{\frac{1}{8}}[/tex]
Therefore, the final exponential equation modelling the given scenario is:
[tex]\implies y=240(2^{\frac{1}{8}})^x[/tex]
[tex]\implies y=240(2)^{\frac{1}{8}x}[/tex]
To find how many bacteria there will be after 4 hours, substitute x = 4 into the found equation:
[tex]\implies y=240(2)^{\frac{1}{8}(4)}[/tex]
[tex]\implies y=240(2)^{\frac{1}{2}}[/tex]
[tex]\implies y=339 \:\: \sf (nearest\:whole\:number)[/tex]
Therefore, there will be 339 bacteria (rounded to the nearest whole number) after 4 hours.
