1.
Two trains A and B are 180km apart.If they start at the
same time and they travel towards each other,they will
meet after 72 minutes.If train A starts 30 minutes earlier,
they will meet after train B has started for 54 minutes.
Find the speeds of the trains.
plz help!!
1d消元法同代入法既問題
2007-03-15 3:09 am
回答 (2)
2007-03-15 3:26 am
✔ 最佳答案
Let x km/hr be the speed of trainA......y km/hr be the speed of trainB
{...(72/60)(x+y)=180----------(1)
{...(30/60)x+(54/60)(x+y)=180------(2)
From (1) , x+y=150-------(3)
From (2) , (1/2)x+(9/10)x+(9/10)y=180
...........................................14x+9y=1800----------(4)
(3)x9:....9x+9y=1350
(4)-(3):...5x=450
..................x=90
Sub. x=90into(3)
x+y=150
90+y=150
y=60
.'.the speed of trainA is 90 km/hr and the speed of trainB is 60 km/hr
2007-03-15 3:28 am
設A的速度是x km/h,B的速度是y km/h
(72/60)x + (72/60)y = 180
x + y = 150
y = 150 - x
(54/60)y + (84/60)x = 180
54y + 84x = 10800
54(150 - x) + 84x = 10800
8100 - 54x + 84x = 10800
30x = 2700
x = 90
y = 60
(72/60)x + (72/60)y = 180
x + y = 150
y = 150 - x
(54/60)y + (84/60)x = 180
54y + 84x = 10800
54(150 - x) + 84x = 10800
8100 - 54x + 84x = 10800
30x = 2700
x = 90
y = 60
參考: EM
收錄日期: 2021-04-12 23:25:17
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