To celebrate Children's Day, Xinhua Bookstore offers children's encyclopedias for 55 yuan per set, buy 4 sets of children's encyclopedias and get 1 set free. How much is it cheaper to buy 4 sets at a time?
新华书店为庆祝"六一"儿童节，儿童百科每套55元，买4套儿童百科送1套．一次买4套，每套便宜多少钱？
<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">55 * (4/5)</gadget>
<output>44</output>

<gadget id="calculator">55 - 44</gadget>
<output>11</output>

<result>11</result>