In a race from point X to poinY and back, Jack averages 30 miles per hour to point Y and 10miles pe
hour back to point X. Sandy averages 20 miles per hour in both directions. Between Jack and Sandy, who finish first?请帮忙翻译,并给出答案,谢谢! 选择题,A. Jack B. Sandy C They tie D. Neither 是同时吗?为何?没想通?