Calculus 1 : Constant of Proportionality

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #31 : How To Find Constant Of Proportionality Of Rate

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:

\(\displaystyle 113\)

\(\displaystyle 2490\)

\(\displaystyle 3175\)

\(\displaystyle 1148\)

\(\displaystyle 33\)

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 #2721 : Functions

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:

\(\displaystyle 3472\)

\(\displaystyle 3933\)

\(\displaystyle 3684\)

\(\displaystyle 4152\)

\(\displaystyle 3200\)

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 #921 : Rate

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:

\(\displaystyle 12964\)

\(\displaystyle 14112\)

\(\displaystyle 13789\)

\(\displaystyle 14852\)

\(\displaystyle 15390\)

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 #3752 : Calculus

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:

\(\displaystyle 1998\)

\(\displaystyle 1724\)

\(\displaystyle 2877\)

\(\displaystyle 896\)

\(\displaystyle 5929\)

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:

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

Example Question #31 : How To Find Constant Of Proportionality Of Rate

The rate of growth of the population of sentient self-replicating toy soldiers is proportional to the population. The population increased from 12 to 43 between Monday and Wednesday. Determine the expected population on Saturday.

Possible Answers:

\(\displaystyle 271\)

\(\displaystyle 253\)

\(\displaystyle 292\)

\(\displaystyle 188\)

\(\displaystyle 207\)

Correct answer:

\(\displaystyle 292\)

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 12 to 43 between Monday and Wednesday, we can solve for this constant of proportionality. Assign the days numbers based on the occurence in the week:

\(\displaystyle 43=12e^{k(4-2)}\)

\(\displaystyle \frac{43}{12}=e^{2k}\)

\(\displaystyle 2k=ln(\frac{43}{12})\)

\(\displaystyle k=\frac{ln(\frac{43}{12})}{2}=0.638\)

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:

\(\displaystyle P=43e^{(7-4)(0.638)} \approx 292\)

Example Question #2723 : Functions

The rate of growth of the prokaryotes of Lake Tahoe is proportional to the population. The population increased from 193678 to 254183 between 2014 and 2015. Determine the expected population in 2021.

Possible Answers:

\(\displaystyle 1398602\)

\(\displaystyle 1200068\)

\(\displaystyle 897775\)

\(\displaystyle 1299915\)

\(\displaystyle 1136241\)

Correct answer:

\(\displaystyle 1299915\)

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 193678 to 254183 between 2014 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 254183=193678e^{k(2015-2014)}\)

\(\displaystyle \frac{254183}{193678}=e^{k}\)

\(\displaystyle k=ln(\frac{254183}{193678})=0.272\)

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:

\(\displaystyle P=254183e^{(2021-2015)(0.272)} \approx 1299915\)

Example Question #931 : Rate

The rate of growth of the alien spores flooding the atmostphere is proportional to the population. The population increased from 19000 to 58000 between 2013 and 2014. Determine the expected population in 2017.

Possible Answers:

\(\displaystyle 1213964\)

\(\displaystyle 1649855\)

\(\displaystyle 2136621\)

\(\displaystyle 2549818\)

\(\displaystyle 1887903\)

Correct answer:

\(\displaystyle 1649855\)

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 19000 to 58000 between 2013 and 2014, we can solve for this constant of proportionality:

\(\displaystyle 58000=19000e^{k(2014-2013)}\)

\(\displaystyle \frac{58}{19}=e^{k}\)

\(\displaystyle k=ln(\frac{58}{19})=1.116\)

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:

\(\displaystyle P=58000e^{(2017-2014)(1.116)} \approx 1649855\)

Example Question #932 : Rate

The rate of growth of the algae in Bill's unkempt swimming pool is proportional to the population. The population increased from 17902 to 39551 between March and May. Determine the expected population in July.

Possible Answers:

\(\displaystyle 87321\)

\(\displaystyle 154479\)

\(\displaystyle 192788\)

\(\displaystyle 102256\)

\(\displaystyle 136894\)

Correct answer:

\(\displaystyle 87321\)

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 17902 to 39551 between March and May, we can solve for this constant of proportionality. Assign the months their number in the calendar to determine time elapsed:

\(\displaystyle 39551=17902e^{k(5-3)}\)

\(\displaystyle \frac{39551}{17902}=e^{2k}\)

\(\displaystyle 2k=ln(\frac{39551}{17902})\)

\(\displaystyle k=\frac{ln(\frac{39551}{17902})}{2}=0.396\)

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:

\(\displaystyle P=39551e^{(7-5)(0.396)} \approx 87321\)

Example Question #933 : Rate

The rate of decrease of the population of Bengal tigers has been proportional to the population. The population decreased from 45000 to 1800 between 1900 and 1972. Determine the constant of proportionality for this decrease.

Possible Answers:

\(\displaystyle 0.0188\)

\(\displaystyle -0.1808\)

\(\displaystyle 0.0039\)

\(\displaystyle -0.0065\)

\(\displaystyle -0.0447\)

Correct answer:

\(\displaystyle -0.0447\)

Explanation:

We're told that the rate of decrease 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 decreased from 45000 to 1800 between 1900 and 1972, we can solve for this constant of proportionality:

\(\displaystyle 1800=45000e^{k(1972-1900)}\)

\(\displaystyle \frac{1800}{45000}=e^{72k}\)

\(\displaystyle 72k=ln(\frac{1800}{45000})\)

\(\displaystyle k=\frac{ln(\frac{1800}{45000})}{72}=-0.0447\)

 

Example Question #934 : Rate

The rate of growth of the population of robomen is proportional to the population. The population increased from 100 units to 1500 between 2008 and 2015. Determine the expected population in 2055.

Possible Answers:

\(\displaystyle 7924462944\)

\(\displaystyle 77812342\)

\(\displaystyle 6012348\)

\(\displaystyle 583094\)

\(\displaystyle 8941326112\)

Correct answer:

\(\displaystyle 7924462944\)

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 100 units to 1500 between 2008 and 2015, we can solve for this constant of proportionality:

\(\displaystyle 1500=100e^{k(2015-2008)}\)

\(\displaystyle 15=e^{7k}\)

\(\displaystyle 7k=ln(15)\)

\(\displaystyle k=\frac{ln(15)}{7}=0.387\)

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:

\(\displaystyle P=1500e^{(2055-2015)(0.387)} \approx 7924462944\)

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