An aircraft flew from A to B at an average speed of 230 mph. It returned from B to A at an average speed of 300 mph. What was its average speed for the two journeys?
260 mph
设飞机从A到B耗时a小时，从B到A耗时b小时，那么可得出230a=300b；飞机飞行整个路程中所用的平均速度则为300b/(a+b) 将两个方程式合并，便可得出平均速度约为260.3 mph 四舍五入后取结果260mph。