Type A flour is 9.5 yuan per bag of 2.5 kg, and type B flour is 21 yuan per bag of 5 kg. Which flour is cheap? How much is cheaper per kilogram?
甲种面粉每袋2.5千克9.5元，乙种面粉每袋5千克21元．哪种面粉便宜？每千克便宜多少元？
<gadget id="calculator">21 / 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">9.5 / 2.5</gadget>
<output>3.8</output>

<gadget id="calculator">(21/5) - 3.8</gadget>
<output>0.4</output>

<result>0.4</result>