The teacher goes to the supermarket to buy footballs, one football is 140 yuan, and the supermarket organizes activities to buy 5 and get 2 free, and buy 25 at a time, how much is each cheaper on average?
老师到超市买足球，一个足球140元，超市搞活动买5赠2，一次买25个，平均每个便宜多少元？
<gadget id="calculator">25 / 5</gadget>
<output>5</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">25 + 10</gadget>
<output>35</output>

<gadget id="calculator">25 / 35</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">140 * (5/7)</gadget>
<output>100</output>

<gadget id="calculator">140 - 100</gadget>
<output>40</output>

<result>40</result>