Apples are 4 yuan per kilogram, and you can buy 4 kilograms and get 1 kilogram free. Xiaohua bought 16 yuan of apples at a time. How much is it cheaper?
苹果每千克4元，一次买4千克送1千克，小华一次买了16元钱的苹果，便宜了多少钱？
<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<result>4</result>