# Derivative Word Problem - US Population

by bobraymund
Tags: derivative, population, word
 P: 27 1. The problem statement, all variables and given/known data (a) Use a graphing calculator or computer to fit an exponential function to the data. Graph the data points and the exponential model. How good is the fit? (b) Estimate the rates of population growth in 1800 and 1850 by averaging slopes of secant lines. (c) Use the exponential model in part (a) to estimate the rates of growth in 1800 and 1850. Compare these estimates with the ones in part (b). (d) Use the exponential model to predict the population in 1870. Compare with the actual population of 38,558,000. Can you explain the discrepancy? 2. Relevant equations Year Population 1790 3,929,000 1800 5,308,000 1810 7,240,000 1820 9,639,000 1830 12,861,000 1840 17,063,000 1850 23,192,000 1860 31,443,000 3. The attempt at a solution I understand part B, you would just do the population in 1800 - population in 1790 all divded by 1800 - 1790... etc. etc.. However, part A and consequently parts C and D are confusing me... Any help would be GREATLY appreciated. Thanks, Bob
 Sci Advisor HW Helper Thanks P: 25,228 You are supposed to use a computer or calculator to do a best fit exponential to the data. You could do this by hand, but it would be tedious and they don't want that. Once you have that fit then you have a model of uniform growth rate over that time. The actual growth rate over any single decade may differ from that average. In particular for d) you are going to find the population growth rate is considerably smaller than you might expect for the period 1860-1870. Did something happen in the US in the decade that might explain it? It's all just about comparing an average growth model with individual data points and figuring out why some of them might not fit the average behavior.
 P: 27 Ok, but how exactly would I fix an exponential to the data? Our teacher gave us the solution as this: Perhaps you could explain exactly what they did? How did they get those numbers in part a?
 Sci Advisor HW Helper Thanks P: 25,228 Derivative Word Problem - US Population They typed the population numbers into a calculator or a computer program. They expect you to be able to do the same. Don't you have one or the other?
 P: 27 Yeah, ha ha, but excuse my "noobness". This is my first calculus course and am still trying to figure out my TI-89. How would I graph the population numbers on my calculator? Would I use the table feature? Thank you for your patience, Bob
HW Helper
Thanks
P: 25,228
 Quote by bobraymund Yeah, ha ha, but excuse my "noobness". This is my first calculus course and am still trying to figure out my TI-89. How would I graph the population numbers on my calculator? Would I use the table feature? Thank you for your patience, Bob
Sorry, I can't help you there. I don't own a calculator that does much more than multiply or divide. I did google and find this. http://www.prenhall.com/esm/app/calc...chskills2.html Does that help? If not I'm sure you can find lots of other stuff on the web.
P: 27
 Quote by Dick Sorry, I can't help you there. I don't own a calculator that does much more than multiply or divide. I did google and find this. http://www.prenhall.com/esm/app/calc...chskills2.html Does that help? If not I'm sure you can find lots of other stuff on the web.
I tried following the instructions on site to plot the points on my TI89 but to no avail.

Any further help is kindly welcome.

-Bob
 Sci Advisor HW Helper Thanks P: 25,228 I'll post a call for help from other homework helpers who might know this stuff.
 Mentor P: 15,170 What instructions did you follow? Those for a linear regression? You are supposed to do an exponential fit. The section of the web page Dick found on nonlinear regression talks about exactly this kind of problem.
P: 27
 Quote by D H What instructions did you follow? Those for a linear regression? You are supposed to do an exponential fit. The section of the web page Dick found on nonlinear regression talks about exactly this kind of problem.
Thank you! I've finally figured it out thanks to the instructions that Dick linked to on that site. Thank you so much for pointing that out.

Ha, I am super happy right now you all have no idea. I was trying to figure this out forever, thank you!

-Bob
 Mentor P: 12,071 For future reference, the manual for the TI-89 is online: http://www.education.ti.com/download...k_Part2_EN.pdf It would be worthwhile for you to download the manual to your computer. The ExpReg function (for fitting an exponential to data) is found on page 819.

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