Aunt Li bought 5 kilograms of apples for 16.5 yuan, and Aunt Liu bought 7 kilograms of apples for 21.7 yuan. Who bought cheap apples? How much cheaper per kilogram?
李阿姨买5千克苹果用去16.5元，刘阿姨买7千克苹果用去21.7元．谁买的苹果便宜？每千克便宜多少钱？
<gadget id="calculator">16.5 / 5</gadget>
<output>3.3</output>

<gadget id="calculator">21.7 / 7</gadget>
<output>3.1</output>

<gadget id="calculator">3.3 - 3.1</gadget>
<output>0.2</output>

<result>0.2</result>