A pair of badminton rackets is 24 yuan, buy 3 pairs and get one free. Teacher Li bought 3 sets at once, how much is each set cheaper?
一副羽毛球拍24元，买3副送一副．李老师一次性买了3副，每副便宜多少钱？
<gadget id="calculator">24 / 3</gadget>
<output>8</output>

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

<gadget id="calculator">24 / 4</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<result>2</result>