Chapter 1, Problem 21P

1. Two scores, X and Y, are recorded for each of n = 4 subjects. For these scores, find the value of each expression.

   ${\displaystyle \sum X}$

   ${\displaystyle \sum Y}$

   ${\displaystyle \sum XY}$

Subject	X	Y
A	3	4
B	0	7
C	−1	5
D	2	2