Xinhua Department Store is running a promotion, 15 yuan per pair of socks, buy 4 pairs and get 1 free. Xiaoli’s mother bought 4 pairs at a time, how much is each pair cheaper?
新华百货商场搞促销活动，每双袜子15元，买4双送1双，小丽妈妈一次买了4双，每双便宜多少钱？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 * (4/5)</gadget>
<output>12</output>

<gadget id="calculator">15 - 12</gadget>
<output>3</output>

<result>3</result>