Find the coordinate of the midpoint of a segment with the endpoints at –9 and 6.

Question

A.1.5
B.–1.5
C.2
D.–3

Answer 1

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.