On the side of the road, there are wooden electric poles every 40 meters, at both ends, a total of 21. Now it is changed to 11 cement poles, including both ends. Find the distance between two adjacent cement poles.
公路的一旁每隔40米有木电杆，两端都有，共21根．现改为水泥电杆11根，包括两端，求两根相邻水泥电杆之间的距离．
<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">11 - 1</gadget>
<output>10</output>

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<result>80</result>