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# Graphing, Trends and Forecasting

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Senior citizens.
The number of senior citizens (65 and over) in the Unites States in millions n years after 1990 can be estimated by using the formula
s= 0.38n + 31.2

(U.S. Bureau of the Census, www.census.gov). The percentage of senior citizens living below the poverty level n years after 1990 can be estimated by using the formula
p= -0.25n + 12.2

a. How many senior citizens were there in 2000?

b. In what year will the percentage of seniors living below the poverty level reach 7%?

c. What is the first year in which we can expect both the number of seniors to be greater than 40 million and fewer than 7% living below the poverty level?

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Graphing, trends and forecasting are investigated.

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The number of senior citizens (65 and over) in the Unites States in millions n years after 1990 can be estimated by using the formula

Senior citizens.
The number of senior citizens (65 and over) in the Unites States in millions n years after 1990 can be estimated by using the formula
s= 0.38n + 31.2

(U.S. Bureau of the Census, www.census.gov). The percentage of senior citizens living below the ...

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• BSc , Wuhan Univ. China
• MA, Shandong Univ.
###### Recent Feedback
• "Your solution, looks excellent. I recognize things from previous chapters. I have seen the standard deviation formula you used to get 5.154. I do understand the Central Limit Theorem needs the sample size (n) to be greater than 30, we have 100. I do understand the sample mean(s) of the population will follow a normal distribution, and that CLT states the sample mean of population is the population (mean), we have 143.74. But when and WHY do we use the standard deviation formula where you got 5.154. WHEN & Why use standard deviation of the sample mean. I don't understand, why don't we simply use the "100" I understand that standard deviation is the square root of variance. I do understand that the variance is the square of the differences of each sample data value minus the mean. But somehow, why not use 100, why use standard deviation of sample mean? Please help explain."
• "excellent work"
• "Thank you so much for all of your help!!! I will be posting another assignment. Please let me know (once posted), if the credits I'm offering is enough or you ! Thanks again!"
• "Thank you"
• "Thank you very much for your valuable time and assistance!"

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