row of poplar trees are planted on both sides of a 90-meter-long tree-lined road at the school gate, both at the beginning and end. A total of 20 trees have been planted. If the distance between two adjacent trees is equal, do you know the distance between two adjacent trees?
校门口一条长90米的林荫路两侧各栽了一行杨树，起点和终点都栽．共栽了20棵，如果相邻两棵树之间的距离相等，你知道相邻两棵树之间的距离吗？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">90 / 9</gadget>
<output>10</output>

<result>10</result>