The cost price of a commodity is 30 yuan each, if it is sold at 30 yuan each, and if it is sold at 40 yuan each, 400 pieces can be sold. When the price of each commodity increases by 1 yuan, the sales volume will decrease by 20. In order to earn the most profit, the selling price should be positioned at how many yuan each.
某商品的成本价为每个30元，如果按每个30元，如果按每个40元卖，可卖出400个．当这种商品每个涨价1元时，销售量就减少20个．为了赚取最多的利润，售价应定位每个多少元．
<gadget id="calculator">20 - 10</gadget>
<output>10</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">40 + 5</gadget>
<output>45</output>

<result>45</result>