Posted by Rachel on .
Find the coordinate of the midpoint of a segment with the endpoints at –9 and 6.
A.1.5
B.–1.5
C.2
D.–3

Geometry 
Steve,
the midpoint is halfway between the two values.
The difference between 9 and 6 is 15. (That is, 6  (9)) Half that difference is 15/2. So, add half the difference to the smaller value:
9 + 15/2 = 3/2
or, subtract half the difference from the larger value:
6  15/2 = 3/2
Or (and this is a much better and simpler way), a value halfway between two other values, a and b, is their average: (a+b)/2
(9+6)/2 = 3/2
So, choice B is correct.