更新1:
2.anne typed 1000words at a speed of 30 words/min,and then typed 750words at a speed of 40 words/min.find her average typing speed.
更新2:
3.joe took 10 minutes to ride a bicycle from home to the shore.the average speed of the whole journey was 600m/min.if his speed in the last 1/3 of his journey was 500m/min. (a)find the time he took in the last 1/3 of his journey (B)find his speed in the remaining journey.