Problem Solving
试题详情
题目：
A certain pilot flew 400 miles to City K at an average speed of 350 miles per hour with the wind and made the trip back at an average speed of 250 miles per hour against the wind. Which of the following is closest to the pilot's average speed, in miles per hour, for the round-trip?
选项:
A、280
B、290
C、300
D、310
E、320
答案:
B
