The density of molten salt mixtures, y g/cm3 , was measured at various temperatures x°C. 

The results were: x 250 270 290 310 330 350 y 1.955 1.935 1.890 1.920 1.895 1.865 

a.Plot a graph of y vs. x showing these points (the graph is called a scatter diagram).

 b. Calculate ∑ x , ∑ y , ∑ x & , ∑ y & , ∑ xy , x̅ , y" 

c. Calculate the regression equation of y on x in the form y = a + bx. Plot this line and the centroidal point on the graph. 

d. For the data given, use a graph to check whether the form of the equation in part (c) represents the data adequately, whether the variance appears to be independent of x, and whether the residuals appear to be normally distributed.