A bottle of beverage is 2 yuan and 40 cents, buy 3 bottles and get one free, buy 3 bottles at a time, how much is each bottle cheaper?
一瓶饮料2元4角，买3瓶送一瓶，一次买3瓶，每瓶便宜多少钱？
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">2 + (2/5)</gadget>
<output>12/5 = around 2.4</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(12/5) * (3/4)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">(12/5) - (9/5)</gadget>
<output>3/5 = around 0.6</output>

<result>3/5 = around 0.6</result>