數學(邏輯)小遊戲

A 城至 B 城的距離為 50 km, 所以整個旅程為 100 km

所以若要整個旅程的平均時速為 100 km/h, 則整個旅程用了的時間需為 1 個小時.

但由於由 A 城至 B 城時已用去了 1 小時, 而回程時必須使用時間 (即使當光速行走), 所以整個旅程用了的時間必超過 1 小時.

所以由 B 城回 A 城時速不論多快都不可能使整個旅程的平均時速為 100 km/h.

To the second answerer.

Distance from A to B = 50(1) km = 50km

If speed of return = 150 km/h
-> the time taken for return trip = 50/150 = 1/3 hour

Average speed of the whole journey
= 100km / (1 + 1/3)hour
= 75 km/h
i.e. The answer you provided is the one which should be considered as ridiculous.

150km/h when returning from b to a

from a to b : 50km using 1h
from b to a : 150km using 1h

(50+150)km/(1+1)h
=average speed of 100km per hour( including the trip from a to b, b to a )

2012-11-24 20:50:40 補充：
翻雷滾天 風卷殘雲 's answer is ridiculous
he doesnt understand the question