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F1 math speed questions

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only need stepsthanks1.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 hrs2.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... 顯示更多 only need steps thanks 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

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(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

其他解答:

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A215E4A27F624C16

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