Each sapling in the nursery is 25 yuan, buy 4 and get 1 free. How much is it cheaper to buy 4 trees at a time?
苗圃场每棵树苗25元，买4棵送1棵．一次性买4棵，每棵便宜多少钱？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">25 * (4/5)</gadget>
<output>20</output>

<gadget id="calculator">25 - 20</gadget>
<output>5</output>

<result>5</result>