Find a cubic function to model the given data. Use 1940 = 0. Use the function to estimate the average monthly Social Security Benefit for a retired worker in 2005.

Average Monthly Social Security Benefits, 1940-1999

Year 1940 1950 1960 1970 1980 1990 2000

Amt in
dollars 23.71 29.03 81.73 123.82 321.10 550.50 757.71

You can easily use Excel or a good calculator to do a cubic regression and solve this.

If you have Excel:

Enter your data into the columns, let column A be for the year and column B for the money.

Click on INSERT, CHART, xy scatter plot, NEXT

Highlight your columns and click NEXT. You can then name the chart, axes, etc. Click FINISH.

Your chart will appear.

Now, click CHART, ADD TRENDLINE, POLYNOMIAL, use 3 for cubic, click OPTIONS and check

the boxes which say, DISPLAY EQUATION ON CHART and DISPLAY R^2 VALUE ON CHART.

click OK and you should be set. Give it a go and let me know how it works out.