一條數學問題
2007-04-18 12:21 am
甲,乙兩列火車從相距180km的兩個城市相向行駛.若它們同時出發,則會於72分鐘後相遇,若甲火車比乙火車早30分鐘出發,則它們會於乙火車出發後54分鐘相遇.求甲,乙兩列火車的速率.
回答 (2)
2007-04-18 12:39 am
✔ 最佳答案
Let X = speed of Train A (Km/min) and Y = speed of Train BThen, 72X + 72Y = 180 ===> 2X + 2Y = 5
and 30X + 54(X + Y) = 180 ===> 84X + 54Y = 180
we multiple the first equation by 27 ====> 54X + 54Y = 135
then second equation minus first equtation, we get 30X = 45
i.e. X = 1.5
by using X=1.5, we can get Y = 1
that means the speed of Train A is 1.5km/min or 90km/hour
and speend of Train B is 1.0km/min or 60km/hour
Hope this can help you.
2007-04-18 12:47 am
Let x km/h = 甲火車的速率
y km/h = 乙火車的速率
72/60 * x + 72/60 * y = 180
x + y = 150
(54+30)/60 * x + 54/60 * y = 180
1.4 x + 0.9 y = 180
1.4 x + 0.9 (150 -x) = 180
1.4 x + 135 - 0.9 x = 180
0.5 x = 45
x = 90 km/h
y = 150 - x = 60 km/h
y km/h = 乙火車的速率
72/60 * x + 72/60 * y = 180
x + y = 150
(54+30)/60 * x + 54/60 * y = 180
1.4 x + 0.9 y = 180
1.4 x + 0.9 (150 -x) = 180
1.4 x + 135 - 0.9 x = 180
0.5 x = 45
x = 90 km/h
y = 150 - x = 60 km/h
參考: me
收錄日期: 2021-05-02 12:33:13
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070417000051KK02051