Question 50335
The number of married couples in the United States in 1995 was 53.9 million. Im 2000, the number of married couples grew to 55.3 million. Write a linear equation that gives the number of married couples in terms of the year. Let x represent the year with x=5 corresponding to 1995.

A linear equation means that as one item independently increases, another item dependently increases.  
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What is independently increasing in your problem?  The years were independently increasing since "time" is not dependent on anything -- it keeps moving forward.
x = time = 1995, 1996, 1997, 1998 ....etc.  Substitute numbers for the year.  So, 1995 = 5
1996 = 6
1997 = 7, etc.
2000 = 10
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What increased dependently upon time?  The number of married couples.
y = 53.9 when x = 1995 = 5 
Point: (5, 53.9)
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y = 55.3 when x = 2000 = 10 
Point: (10, 55.3)
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Use the slope-intercept form as your formula for a line (or linear equation)]
y=mx+b [We need the slope(m) and the y-intercept (b)]
Slope = m = (y2-y1)/x2-x1) 
Slope = m = (55.3-53.9)/10-5) [Plug-in the points.
Slope = m =1.4/5 = 0.28
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y=mx+b
55.3=(.28)(10)+b [Plug-in the known values and solve for b]

55.3-2.8=2.8-2.8+b
52.5=b
y=.28x+52.5 [Plug-in the values for the slope (m) and the y-intercept (b)for the equation of the line]
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To find out the number of married couples for any given year, just plug-in the year (x) and solve for the number of couples.