A batch of vegetables is shipped from the store, among which cucumbers account for (1/5) of the total, tomatoes account for (2/5) of the total, and the rest are potatoes. What percentage of this batch of vegetables do potatoes account for?
商店运来一批蔬菜，其中黄瓜占总数的(1/5)，西红柿占总数的(2/5)，其它的是土豆，土豆占这批蔬菜的几分之几？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/5) - (2/5)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>