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A researcher wishes to study how the average weight Y (in kilograms) of children changes during the first year of life. He plots these averages versus the age X (in months) and decides to fit a least-squares regression line to the data with X as the explanatory variable and Y as the response variable. He computes the following quantities.
r = correlation between X and Y = 0.9 J = mean of the values of X = 6.5
M = mean of the values of Y = 6.6 Sx = standard deviation of the values of X = 3.6
Sy = standard deviation of the values of Y = 1.2
The slope of the least-squares line is