Question: how to calculate the slope of the least-squares regression line?
Answer: Step 1: For each (x,y) point calculate x2 and xy.
Step 2: Sum all x, y, x2 and xy, which gives us Σx, Σy, Σx2 and Σxy (Σ means "sum up")
Step 3: Calculate Slope m:
m = N Σ(xy) − Σx Σy N Σ(x2) − (Σx)2
Step 4: Calculate Intercept b:
b = Σy − m Σx N.
Step 5: Assemble the equation of a line.