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?

A. 60 km/hr B. 60 5 /123 km/hr C. 62 km/hr D. 65 5/123 km/hr

Answer Answer: Option D Explanation: 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

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

A. 10.4 km/hr B. 10.8 km/hr C. 11 km/hr D. 12.2km/hr

Answer Answer: Option B Explanation: 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

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:

A. 45 km/hr B. 47.5 km/hr C. 52 km/hr D. 56.25 km/hr

Answer Answer: Option D Explanation: 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

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?

A. 5 km B. 5.5 km C. 6 km D. 6.5 km

Answer Answer: Option C Explanation: 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