A box of yogurt is 30 yuan. The dairy shop is doing promotional activities. Buy 5 boxes and get 1 box free. Aunt Wang bought 6 boxes. How much is each box cheaper?
一箱酸奶30元，牛奶店做促销活动，买5箱送1箱，王阿姨买了6箱，每箱相当于便宜了多少钱？
<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">30 * (5/6)</gadget>
<output>25</output>

<gadget id="calculator">30 - 25</gadget>
<output>5</output>

<result>5</result>