A batch of vegetables is shipped from the store. Cucumbers account for 1/5 of the total, tomatoes account for 3/10 of the total, and potatoes account for the rest. What percentage of the batch of vegetables do potatoes account for?
商店运来一批蔬菜，黄瓜占总数的(1/5)，西红柿占总数的(3/10)，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">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/5) - (3/10)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>