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1.John cycled 47km in 5 hours,sometimes at the speed of 8km/hr and sometimes at10km/hr.For how long had he ridden at the faster speed?
(ans:3.5 hrs
2.A man drove at a uniform speed for 2hours.Then he reduced the speed by 12km/hr for 1.5hours.The total distance travelled was 277km.Find his initial speed.
(ans:70km/hr
3 Two cities,A and B,are480km apart.Car P travels form A to B while car Q travels from B to A,and the speed of car P is twice the speed of car Q.If they meet each other on the way after 4 hours, how far is the meeting place from city B?
(ans:160km
4 A boy can ride at an average speed of 11km per hour from A to B and then back in a certain time.If he rode from A to B at 8km per hour ,and returned at 12km/hr,he would spend 21mins.more on the double journey.Find the distance between A and B.
(ans:13.2km
5 Benson drove home for lunch at 72km/hr .He took 45mins. for his meal and drove back to office at 48km/hr .He was absent from office for 2 hours altogether.Find the distance between his home and the office.
(ans:36km
F1 math speed questions
2010-01-22 7:45 am
回答 (2)
2010-01-22 8:17 am
✔ 最佳答案
(1) Let the time for 10km/h be x hours.Then the time for 8km/h is 5 – x hours
Total distance travelled = 10x + 8(5 – x) = 47
10x + 40 – 8x = 47
2x = 7
x = 3.5
He had ridden at the faster speed for 3.5 hours
(2) Let the initial speed be x km/h
The reduced speed is x – 12 km/hr
Total distance travelled = 2x + 1.5(x – 12) = 227 (typo in question)
2x + 1.5x – 18 = 227
3.5x = 245
x = 70
His initial speed is 70 km/h
(3) Let the distance of the meeting place from city B be x km
Then it is 480 – x km from city A
Since speed P : speed Q = 2 : 1
Distance from city A : distance from city B = 2 : 1
Hence (480 – x)/x = 2
480 – x = 2x
480 = 3x
x = 160
The distance of the meeting place from city B is 160 km
(4) Let the distance be x km.
Time to travel at uniform speed of 11km/h = 2x/11
Time to travel if travelled at 8km/h and 12km/h = x/8 + x/12
x/8 + x/12 – 2x/11 = 21/60
33x/264 + 22x/264 – 48x/264 = 7/20
7x/264 = 7/20
x = 264/20 = 13.2
The distance is 13.2 km
(5) Let the distance be x km.
Total time spent = x/72 + 45/60 + x/48 = 2
2x/144 + 3x/144 = 2 – 3/4
5x/144 = 5/4
x = 144/4 = 36
The distance is 36 km
2010-01-22 8:35 am
1.
let x hours that he had ridden in 10km/hr so he had ridden (5-x)hours in 8km/hr.
10x+(5-x)8=47
10x+40-8x=47
2x=7
x=3.5
3.
let the speed of car c is x km/hr,then the speed of car p is 2x km/hr.
(x+2x)4=480
3x=120
x=40
so the speed of car c is 40 km/hr
since car c meet car p from city b to city a
so the distance of the meeting place from city B:
(40x4)km=160km
4.let the distance be x km.
hours it takes to ride in the average speed once:x/11
hours it takes to ride in the 8km:x/8
hours it takes to ride in the12km:x/12
[(x/8)+(x/12)]-2(x/11)=21/60
33x+22x-48x
------------------- =0.35
264
7x =92.4
x =13.2
5.let xhr be the time he drove to the home
and (2-x-45/60) be the time he drove to the office
72x=48(2-x-45/60)
72x=48(1.25-x)
72x=60-48x
120x=60
x=0.5
distance:(72x0.5)km=36km
2010-01-22 00:36:46 補充：
= =天呀上面寫左277~...計唔到
let x hours that he had ridden in 10km/hr so he had ridden (5-x)hours in 8km/hr.
10x+(5-x)8=47
10x+40-8x=47
2x=7
x=3.5
3.
let the speed of car c is x km/hr,then the speed of car p is 2x km/hr.
(x+2x)4=480
3x=120
x=40
so the speed of car c is 40 km/hr
since car c meet car p from city b to city a
so the distance of the meeting place from city B:
(40x4)km=160km
4.let the distance be x km.
hours it takes to ride in the average speed once:x/11
hours it takes to ride in the 8km:x/8
hours it takes to ride in the12km:x/12
[(x/8)+(x/12)]-2(x/11)=21/60
33x+22x-48x
------------------- =0.35
264
7x =92.4
x =13.2
5.let xhr be the time he drove to the home
and (2-x-45/60) be the time he drove to the office
72x=48(2-x-45/60)
72x=48(1.25-x)
72x=60-48x
120x=60
x=0.5
distance:(72x0.5)km=36km
2010-01-22 00:36:46 補充：
= =天呀上面寫左277~...計唔到
收錄日期: 2021-04-15 17:15:43
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