A small-displacement car consumes 6 liters of gasoline per 100 kilometers traveled, and another large-displacement car consumes 10 liters of gasoline per 100 kilometers traveled. The two cars go from Qingxian to Beijing at the same time, and they both drive when they return to Qingxian. After traveling 500 kilometers, how many liters of fuel is saved by a small-displacement car compared with a large-displacement car?
一款小排量汽车每行驶100千米消耗汽油6升，另一款大排量汽车每行驶100千米消耗汽油10升，两辆汽车同时从青县去北京，到返回青县时都行驶了500千米，小排量汽车比大排量汽车总共省油多少升？
<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<gadget id="calculator">500 / 100</gadget>
<output>5</output>

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

<result>20</result>