87. Reconsider the situation of Exercise 73, in which x

retained austenite content using a garnet abrasive and y

abrasive wear loss were related via the simple linear regression model Y

0
1x . Suppose that for a second type of abrasive, these variables are also related via the simple linear regression model Y
0 1x 

and that V(!)
2 for both types of abrasive. If the data set consists of n1 observations on the first abrasive and n2 on the second and if SSE1 and SSE2 denote the two error sums of squares, then a pooled estimate of 2 is ˆ2
?