On both sides of a 120-meter-long bridge, there are 42 colored lanterns hung at the bridge head and the end of the bridge. Given that the distances between two adjacent colored lanterns are equal, find the distance between the two colored lanterns.
在一座长120米的大桥两边挂彩灯，桥头和桥尾，一共挂了42盏彩灯．已知相邻两盏彩灯之间的距离相等，求两盏彩灯之间的距离．
<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">120 / 20</gadget>
<output>6</output>

<result>6</result>