InaracefrompointXtopoinYandback,Jackaverages30milesperhourtopointYand10milespehourbacktopointX.Sandyaverages20milesperhourinbothdirections.BetweenJackandSandy,whofinishfirst?请帮忙翻译,并给出答案,A.Jack

Question

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,
A.Jack B.Sandy C They tie D.Neither
为何？没想通？

Answer 1

翻译：在一场从X点到Y点然后再返回的比赛中,杰克以平均每小时30公里的速度到达Y点,然后又以每小时10公里的速度到达X点.Sandy来回平均每小时20公里的速度.在杰克和Sandy之间,谁第一个完成?
答案：Sandy先达到.
答案解析：设X点到Y点之间的距离为S,则,
S/30 + S/10 >2S/20
即Jack所用的时间比Sandy的时间多.Sandy先到达.