A bus travels from city A to city B. It takes 5 hours to drive 80 kilometers per hour, but it takes 1 hour less to return. What is the speed of the bus?
一辆客车从甲城开往乙城，每小时行驶80千米，用了5小时，返回时少用了1小时，这辆客车返回的速度是多少？
<gadget id="calculator">80 * 5</gadget>
<output>400</output>

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

<gadget id="calculator">400 / 4</gadget>
<output>100</output>

<result>100</result>