A bag of flour is 42 yuan, buy 5 bags and get 2 bags free, how much is each bag cheaper?
一袋面粉42元，买5袋送2袋，算一算每袋便宜了多少钱？
<gadget id="calculator">5 + 2</gadget>
<output>7</output>

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

<gadget id="calculator">42 * (5/7)</gadget>
<output>30</output>

<gadget id="calculator">42 - 30</gadget>
<output>12</output>

<result>12</result>