2 yuan per bottle of mineral water. Buy 9 bottles and get 1 bottle free, buy 9 bottles at a time, how much is each bottle cheaper?
每瓶矿泉水2元．买9瓶送1瓶，一次买9瓶，每瓶便宜多少元？
<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">9 * (1/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">2 - (9/5)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>