The** segment addition postulate **is a fairly obvious-seeming postulate which states that:

If a point *B* lies on a line segment , then .

That is, the distance from one endpoint to the other is the sum of the distances from the middle point to either endpoint.

**Example:**

Find the length *XY* in the figure shown.

By the Segment Addition Postulate, .

Substitute the given values.

Solve for *XY*.