Ginza Supermarket launched a promotion on May Day. Each pair of socks is 12 yuan. Buy 3 pairs and get 1 free. Uncle Li bought 3 pairs at a time. How much is each pair of socks cheaper?
银座超市五一开展促销活动，袜子每双12元，买3双送1双，李叔叔一次买了3双，每双袜子便宜多少钱？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">12 * (1/3)</gadget>
<output>4</output>

<result>4</result>