Uncle Li went to buy saplings. The nursery is holding an event. Each sapling is 20 yuan, buy 3 get 1 free, buy 3 lessons at a time, how much is each sapling cheaper?
李叔叔去买树苗，苗圃正在搞活动，每颗树苗20元，买3送1，一次买3课，每颗便宜多少钱？
<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">20 * (3/4)</gadget>
<output>15</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<result>5</result>