1.a student cycles home to lunchat 12km/h,takes half an hour for his lunch,and cycles back to school at 10km/h.he is absent from school for 57.5 minutesaltogether.how far from his home is the school?
2.a boy walks to school at 3.5km/h and is one minutes late.if he walked at 3and one-third(三又三分一)km/h he would have been 3 minutes late .find the distance to the school.
Maths
2008-01-02 5:01 am
回答 (2)
2008-01-02 6:40 am
✔ 最佳答案
1. Let x be the distance between school and home, then:x/12 + x/10 = (57.5-30)/60
(10x + 12x) /120 = 27.5 / 60
22x = 55
x = 2.5 km
2. Let x be the distance to school, then:
x/(3+1/3) - x/3.5 = 2/60
(3.5x - (3+1/3)x ) / (35/3) = 2/60
(0.5/3)x = 35/90
x = (2+1/3) km (二又三分一公里)
參考: 自己
2008-01-02 7:37 am
1)
School ------> Home : 12km/h * (X hours)
Have lunch at Home : 0.5 hour
Home ------> School : 10km/h * (Y hours)
Since Distance between Home and School is same : 12*X = 10* Y
total = 57.5/60 (in hour)
57.5/60 = 12*X + 0.5 + 10*Y
23/24 = 12*X + 12/24 + 10*Y
11/24 = 12*X + 10*Y
so 11/24 = (10*Y) + 10*Y
11/24 = 20*Y
Y = 11/480 hour
Distance = 10*Y
= 10*11/480
= 11/48 km
2.
Let T = Expired Time - Starting Time
3.5km/h*(T hour+1 minute) = 10/3 km/h * (T hour+3 minute)
3.5 * (T+1/60) = 10/3 * (T+1/20)
T*3.5 + 3.5/60 = T*10/3 + 1/6
T*105/30 + 35/600 = T*100/30 + 100/600
T*105/30 - T*100/30 = 100/600 - 35/600
T*1/6 = 65/600
T = 390/600
T = 0.65 hour
= 39 minutes
Distance = 3.5*(39+1)/60
= 7/3 km
= 2.3333 km
School ------> Home : 12km/h * (X hours)
Have lunch at Home : 0.5 hour
Home ------> School : 10km/h * (Y hours)
Since Distance between Home and School is same : 12*X = 10* Y
total = 57.5/60 (in hour)
57.5/60 = 12*X + 0.5 + 10*Y
23/24 = 12*X + 12/24 + 10*Y
11/24 = 12*X + 10*Y
so 11/24 = (10*Y) + 10*Y
11/24 = 20*Y
Y = 11/480 hour
Distance = 10*Y
= 10*11/480
= 11/48 km
2.
Let T = Expired Time - Starting Time
3.5km/h*(T hour+1 minute) = 10/3 km/h * (T hour+3 minute)
3.5 * (T+1/60) = 10/3 * (T+1/20)
T*3.5 + 3.5/60 = T*10/3 + 1/6
T*105/30 + 35/600 = T*100/30 + 100/600
T*105/30 - T*100/30 = 100/600 - 35/600
T*1/6 = 65/600
T = 390/600
T = 0.65 hour
= 39 minutes
Distance = 3.5*(39+1)/60
= 7/3 km
= 2.3333 km
收錄日期: 2021-04-13 14:50:57
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080101000051KK03929