In statistics how do I solve Exy?

Answer 1

The summation notation may be used not only with single variables, but with algebraic expressions containing more than one variable. When these expressions are encountered, considerable attention must be paid to where the parentheses are located. If the parentheses are located after the summation sign, then the general rule is: DO THE ALGEBRAIC OPERATION AND THEN SUM. For example, suppose that X is the score on first homework and Y is the score for the second and that the gradebook is as follows:

X

Y

5

6

7

7

7

8

6

7

8

8

The sum of the product of the two variables could be written:

The preceding sum may be most easily computed by creating a third column on the data table above:

X

Y

X * Y

5

6

30

7

7

49

7

8

56

6

7

42

8

8

64

33

36

241