If trees are planted on both sides of a 100-meter-long road, and a tree is planted every 5 meters from the beginning to the end, how many trees can be planted in total?
在一条长100米的马路两边栽树，从头到尾每隔5米栽一棵树，一共可以栽多少棵树．
<gadget id="calculator">100 / 5</gadget>
<output>20</output>

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

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

<result>42</result>