16.  A man travels 600 km by train at 80 km per hour 800 km by ship at 40 km per hour, 500 km by aeroplane at 400 km/hr and 100 km by car at 50 km per hour. What is the average speed for the entire distance?


60 km/hr
60 5 /123 km/hr
62 km/hr
65 5/123 km/hr


Answer

 Option

Total distance traveled = (600+800+500+500+100) km = 2000 km Total time taken = (600/80 + 800/40 + 500/400 + 100/50)hrs = 123/4 hrs Average speed = (2000*4/123)km/hrs = ( 8000/123) km/hr = 65 5/123 km/hr

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17.  A boy rides his bicycle 10 km at on average speed of 12 km per hour and again travels 12 km at on average speed of 10 km/hr.His average speed for the entered trip is approximately


10.4 km/hr
10.8 km/hr
11 km/hr
12.2km/hr


Answer

 Option

Total distance travel = (10+12) km/hr = 22km/hr Total time taken =(10/12 + 12/10) hours = 61/30 hrs Average speed = (22*30/61)km/hr = 10.8 km/hr

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18.  A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:


35 km/hr
35.5 km/hr
36 km/hr
71.11 km/hr


Answer

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Total time taken = (160/64 + 160/8) hrs = 9/2 hrs Average speed =(320*2/9) km/hr = 71.11 km/hr

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19.  The average speed of a train in the onward journey is 25% more than that in the return journey. The train halts for 1 hour on reaching the destination. The total time taken for the complete to and from journey is 17 hours, covering a distance of 800 km.The speed of the train in onward journey is:


45 km/hr
47.5 km/hr
52 km/hr
56.25 km/hr


Answer

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Let the speed in return journey be x km/hr Then speed in onward journey = 125/100 x = (5/4 x) km/hr Average speed = (2*5/4 x* x / 5/4 x+x) km/hr = 10x/9 km/hr (800 * 9/10x) = 16 = x =(800*9/16*10) = 45 So speed in onward journey = (5/4 *45) km/hr = 56.25 km/hr

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20.  A boy goes to his school from his house at a speed of 3 km/hr and returns at a speed of 2 km/hr.If he takes 5 hours in going and coming,the distance between his house and school is?


5 km
5.5 km
6 km
6.5 km


Answer

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Average speed = (2*3*2/3+2) km/hr = 12/5 km/hr Distance traveled = (12/5 * 5)km = 12 km Distance between house and school = 12/2 = 6

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