A car drives from A to B at 60 km/h for 3 hours. 90 kilometers per hour when returning. Find the average speed of this car for the whole round trip?
一辆汽车从甲地开往乙地，去时每小时60千米，行驶了3小时．返回时每小时90千米．求这辆汽车往返全程的平均速度？
<gadget id="calculator">60 * 3</gadget>
<output>180</output>

<gadget id="calculator">180 / 90</gadget>
<output>2</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">180 * (2/5)</gadget>
<output>72</output>

<result>72</result>