Question

In the xy-plane, the point (6,3) is the midpoint of the line segment with endpoints (x,5) and (9,y). What is the value of x+y?

Answer 1

The formula for the midpoint of a line is 
x1 + x2            y1 + y2
---------   ,        -----------
     2                     2

so x+9 / 2 = 6  and     5+y / 2 = 3

so x = 3 and y =  1

x+y = 4