Calculus 1 : Rate

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #25 : How To Find Constant Of Proportionality Of Rate

The rate of growth of the number of fungal cells on a loaf of bread is proportional to the population. The population increased from 112 to 357 between 1:00 and 2:00. What is the expected population at 3:00?

Possible Answers:

\(\displaystyle 1412\)

\(\displaystyle 839\)

\(\displaystyle 602\)

\(\displaystyle 1138\)

\(\displaystyle 1387\)

Correct answer:

\(\displaystyle 1138\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 112 to 357 between 1:00 and 2:00, we can solve for this constant of proportionality:

\(\displaystyle 357=112e^{k(2-1)}\)

\(\displaystyle \frac{357}{112}=e^{k}\)

\(\displaystyle k=ln(\frac{357}{112})\)

\(\displaystyle k=1.159\)

Using this, we can calculate the expected value from 2:00 to 3:00:

\(\displaystyle P=357e^{(3-2)(1.159)} \approx 1138\)

Example Question #26 : How To Find Constant Of Proportionality Of Rate

The rate of growth of the bacteria in a petri dish is proportional to the population. The population increased from 29 to 167 between 3:00 and 6:00. What is the expected population in 8:30?

Possible Answers:

\(\displaystyle 912\)

\(\displaystyle 365\)

\(\displaystyle 719\)

\(\displaystyle 848\)

\(\displaystyle 640\)

Correct answer:

\(\displaystyle 719\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 29 to 167 between 3:00 and 6:00, we can solve for this constant of proportionality:

\(\displaystyle 167=29e^{k(6-3)}\)

\(\displaystyle \frac{167}{29}=e^{3k}\)

\(\displaystyle 3k=ln(\frac{167}{29})\)

\(\displaystyle k=\frac{ln(\frac{167}{29})}{3}=0.584\)

Using this, we can calculate the expected value from 6:00 to 8:30:

\(\displaystyle P=167e^{(8.5-6)(0.584)} \approx 719\)

Example Question #21 : Constant Of Proportionality

The rate of decrease due to poaching of the elephants in unprotected Sahara is proportional to the population. The population in one region decreased from 1038 to 817 between 2010 and 2015. What is the expected population in 2017?

Possible Answers:

\(\displaystyle 493\)

\(\displaystyle 619\)

\(\displaystyle 527\)

\(\displaystyle 779\)

\(\displaystyle 742\)

Correct answer:

\(\displaystyle 742\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population decreased from 1038 to 817 between 2010 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 817=1038e^{k(2015-2010)}\)

\(\displaystyle \frac{817}{1038}=e^{5k}\)

\(\displaystyle 5k=ln(\frac{817}{1038})\)

\(\displaystyle k=\frac{ln(\frac{817}{1038})}{5}=-0.048\)

Using this, we can calculate the expected value from 2015 to 2017:

\(\displaystyle P=817e^{(2017-2015)(-0.048)} \approx 742\)

Example Question #28 : How To Find Constant Of Proportionality Of Rate

The rate of decrease in the population of grey wolves in Tennessee is proportional to the population. The population decreased from 5430  to 3740 between 2008 and 2015. What is the expected population in 2020?

Possible Answers:

\(\displaystyle 3128\)

\(\displaystyle 2972\)

\(\displaystyle 3396\)

\(\displaystyle 2430\)

\(\displaystyle 2865\)

Correct answer:

\(\displaystyle 2865\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population decreased from 5430  to 3740 between 2008 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 3740=5430e^{k(2015-2008)}\)

\(\displaystyle \frac{3740}{5430}=e^{7k}\)

\(\displaystyle 7k=ln(\frac{3740}{5430})\)

\(\displaystyle k=\frac{ln(\frac{3740}{5430})}{7}=-0.0533\)

Using this, we can calculate the expected value from :

\(\displaystyle P=3740e^{(2020-2015)(-0.0533)} \approx 2865\)

Example Question #29 : How To Find Constant Of Proportionality Of Rate

The rate of growth of the population of prokaryotes in a pond is proportional to the population. The population increased from 1130 to 1460 between 3:15 and 4:30. What is the expected population in 6:45?

Possible Answers:

\(\displaystyle 2688\)

\(\displaystyle 2495\)

\(\displaystyle 2208\)

\(\displaystyle 2316\)

\(\displaystyle 2127\)

Correct answer:

\(\displaystyle 2316\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 1130 to 1460 between 3:15 and 4:30, we can solve for this constant of proportionality. Convert the minutes to decimal values of an hour:

\(\displaystyle 1460=1130e^{k(4.5-3.25)}\)

\(\displaystyle \frac{1460}{1130}=e^{1.25k}\)

\(\displaystyle 1.25k=ln(\frac{1460}{1130})\)

\(\displaystyle k=\frac{ln(\frac{1460}{1130})}{1.25}=0.205\)

Using this, we can calculate the expected value from 4:30 to 6:45:

\(\displaystyle P=1460e^{(6.75-4.5)(0.205)} \approx 2316\)

Example Question #30 : How To Find Constant Of Proportionality Of Rate

The rate of growth of the constituency of the hivemind is proportional to the population. The population increased from 10800 to 25200 between April and June. What is the expected population in November, when mankind takes its last stand?

Possible Answers:

\(\displaystyle 187450\)

\(\displaystyle 163689\)

\(\displaystyle 119368\)

\(\displaystyle 144255\)

\(\displaystyle 209945\)

Correct answer:

\(\displaystyle 209945\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 10800 to 25200 between April and June, we can solve for this constant of proportionality. Use the months' number in the calendar:

\(\displaystyle 25200=10800e^{k(6-4)}\)

\(\displaystyle \frac{25200}{10800}=e^{2k}\)

\(\displaystyle 2k=ln(\frac{25200}{10800})\)

\(\displaystyle k=\frac{ln(\frac{25200}{10800})}{2}=0.424\)

Using this, we can calculate the expected value in November from June:

\(\displaystyle P=25200e^{(11-6)(0.424)} \approx 209945\)

Good luck, humanity.

Example Question #31 : Constant Of Proportionality

The rate of decrease of baceterial cells in response to a new antibiotic is proportional to the population. The population decreased from 15800 to 6540 between 3:15 and 4:00. What is the expected population at 8:30?

Possible Answers:

\(\displaystyle 33\)

\(\displaystyle 113\)

\(\displaystyle 2490\)

\(\displaystyle 1148\)

\(\displaystyle 3175\)

Correct answer:

\(\displaystyle 33\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population decreased from 15800 to 6540 between 3:15 and 4:00, we can solve for this constant of proportionality. Treat the minutes as decimal values for the hour:

\(\displaystyle 6540=15800e^{k(4-3.25)}\)

\(\displaystyle \frac{6540}{15800}=e^{0.75k}\)

\(\displaystyle 0.75k=ln(\frac{6540}{15800})\)

\(\displaystyle k=\frac{ln(\frac{6540}{15800})}{0.75}=-1.176\)

Using this, we can calculate the expected value from 4:00 to 8:30:

\(\displaystyle P=6540e^{(8.5-4)(-1.176)} \approx 33\)

Example Question #32 : Constant Of Proportionality

The rate of growth of the population of electric mice in Japan is proportional to the population. The population increased from 1800 to 2500 between 2012 and 2015. Determine the expected population in 2018.

Possible Answers:

\(\displaystyle 3200\)

\(\displaystyle 3933\)

\(\displaystyle 3684\)

\(\displaystyle 3472\)

\(\displaystyle 4152\)

Correct answer:

\(\displaystyle 3472\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, \(\displaystyle t\)  represents a measure of elapsed time relative to this population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 1800 to 2500 between 2012 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 2500=1800e^{k(2015-2012)}\)

\(\displaystyle \frac{25}{18}=e^{3k}\)

\(\displaystyle 3k=ln(\frac{25}{18})\)

\(\displaystyle k=\frac{ln(\frac{25}{18})}{3}=0.1095\)

Now that the constant of proportionality is known, we can use it to find an expected population value relative to an initial population value due to the difference in time points:

\(\displaystyle P=2500e^{(2018-2015)(0.1095)} \approx 3472\)

Example Question #33 : Constant Of Proportionality

The rate of growth of the bacteria in a petri dish is proportional to the population. The population increased from 4900 to 7193 between 3:54 and 4:21. Determine the expected population at 5:12.

Possible Answers:

\(\displaystyle 14112\)

\(\displaystyle 13789\)

\(\displaystyle 12964\)

\(\displaystyle 14852\)

\(\displaystyle 15390\)

Correct answer:

\(\displaystyle 14852\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, \(\displaystyle t\)  represents a measure of elapsed time relative to this population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 4900 to 7193 between 3:54 and 4:21, we can solve for this constant of proportionality. Treat the minutes as decimals of an hour by dividing by 60:

\(\displaystyle 7193=4900e^{k(4.35-3.9)}\)

\(\displaystyle \frac{7193}{4900}=e^{0.45k}\)

\(\displaystyle 0.45k=ln(\frac{7193}{4900})\)

\(\displaystyle k=\frac{ln(\frac{7193}{4900})}{0.45}=0.853\)

Now that the constant of proportionality is known, we can use it to find an expected population value relative to an initial population value due to the difference in time points:

\(\displaystyle P=7193e^{(5.20-4.35)(0.853)} \approx 14852\)

Example Question #34 : Constant Of Proportionality

The rate of growth of the yeast in a loaf of bread is proportional to the population. The population increased from 178 to 413 between 3:15 and 3:45. Determine the expected population at 5:20.

Possible Answers:

\(\displaystyle 1998\)

\(\displaystyle 896\)

\(\displaystyle 2877\)

\(\displaystyle 1724\)

\(\displaystyle 5929\)

Correct answer:

\(\displaystyle 5929\)

Explanation:

We're told that the rate of growth of the population is proportional to the population itself, meaning that this problem deals with exponential growth/decay. The population can be modeled thusly:

\(\displaystyle p(t)=p_0e^{kt}\)

Where \(\displaystyle p_0\) is an initial population value, \(\displaystyle t\)  represents a measure of elapsed time relative to this population value, and \(\displaystyle k\) is the constant of proportionality.

Since the population increased from 178 to 413 between 3:15 and 3:45, we can solve for this constant of proportionality. Treat the minutes as decimals after the hour by dividing them by 60:

\(\displaystyle 413=178e^{k(3.75-3.25)}\)

\(\displaystyle \frac{413}{178}=e^{0.5k}\)

\(\displaystyle 0.5k=ln(\frac{413}{178})\)

\(\displaystyle k=\frac{ln(\frac{413}{178})}{0.5}=1.683\)

Now that the constant of proportionality is known, we can use it to find an expected population value relative to an initial population value due to the difference in time points:

\(\displaystyle P=413e^{(5.333-3.75)(1.683)} \approx 5929\)

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