1.Lily drives a car at a speed of 100km/h for 200km.then at a speed of 120km/h for 360km.Find the average of lily foe completing the journey.
2.Sally drives a car at a speed of 80km/h from city A to city B.At the same time,Bonnie and Connie drive at a speed of 60km/h and 65km/h respectively from city B to city A.If Sally metts Bonnie 30 mintues after she has met Connie,find the distance between city A and B.
數學高手請進....F.1女有難.....2條..
2009-03-12 3:48 am
回答 (2)
2009-03-12 4:01 am
✔ 最佳答案
1 Lily uses 200/100=2 hours in her first travelling and she uses 360/120=3 hours in her second travelling. Total travelling time = 2+3=5 hoursAverage speed = Total distance/ Total time = (360+200)/5= 112 km/h
2 Let the distance between city A and B is L and the meeting time of Sally and Connie is T
Then 80T+65T=L...(1)
80(T+0.5)+60(T+0.5)=L...(2)
So L+40-5T+30=L=>T=12
L= 1740 km
2009-03-11 20:02:06 補充：
Sorry T=14 and L=2030 km
2009-03-12 5:06 am
1.The average of lily foe completing the journey
=(200+360)/(200/100+360/120)
=560/(2+3)
=560/5
=112km/h
2.The distance between city A and B
=30/60(80+65)
=72.5
2009-03-11 21:07:07 補充：
72.5km
=(200+360)/(200/100+360/120)
=560/(2+3)
=560/5
=112km/h
2.The distance between city A and B
=30/60(80+65)
=72.5
2009-03-11 21:07:07 補充：
72.5km
參考: me
收錄日期: 2021-04-26 13:05:38
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