A scientist is observing the growth of a bacterial culture. The number of bacteria after hours is modeled by an exponential function of the form
The scientist records that after hours the culture contains bacteria.
Which equation best models the number of bacteria after hours?
For an exponential model of the form , use the initial value to identify , then substitute the additional data point to solve for . If the choices use rounded growth factors, calculate accurately and round it to the same place value before matching the model; also verify that the selected model keeps the correct initial value.
Hints
Plug in the known values
Use the model and substitute the recorded values and .
Isolate
After substituting, divide both sides of the equation by to find the value of .
Find the growth factor
Take the cube root of the value you found for . Then consider how that decimal rounds to the same number of decimal places used in the answer choices.
Check the initial value
The coefficient in the model represents the number of bacteria when . Make sure the selected equation preserves the given starting value.
Desmos Guide
Compute the growth factor
In Desmos, enter . The result is approximately , the value of that satisfies .
Match the rounded value to a choice
Round the Desmos result to the nearest hundredth, since the growth factors in the choices are written to that precision. Then select the equation that also has as its initial value.
Step-by-step Explanation
Use the given data point to set up an equation
The model has the form .
After hours, the culture contains bacteria, so substitute and :
Solve for the growth factor
Divide both sides by :
Take the cube root:
Round to match the choices
The growth factors in the choices are given to the nearest hundredth. Since rounds to , the best model is
This is choice D.