If there are 5 points in the middle of a line segment, how many line segments can these 7 points form?
在一条线段的中间，另有5个点，则这7个点可以组成多少条线段．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">7 * 6</gadget>
<output>42</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>