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Example of equations
You have seen that a 60-year-old typist scored 100, while a 20-year-old typist scored 50 on a typing test. Calculate the equation for the line that passes through these points.
First you find the slope:
slope = (y2 - y1) / (x2 - x1)
slope = (50 - 100) / (20 - 60)
slope = -50 / -40
slope = 1.25
Now plug this slope plus one of the points into the straight-line equation to find b, the y-intercept:
y = mx + b
100 = 1.25(60) + b
100 = 75 + b
b = 25
The equation of the straight line that passes through (60,100) and (20,50) is:
y = 1.25x + 25
To check, plug in the numbers from the second point on the line:
y2 = b + mx2
50 = 25 + (1.25 x 20)
50 = 50
Correct!
Memory Jogger
Find the equation of a line with a slope of 3 that passes through the point (2,1):
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