M4maths Previous Puzzles

17 Jan 2022 Time Distance & Speed

Mohit covered a distance of 360 km between two cities, taking a total of 13 hours 30 minutes. If part of the distance was covered at 50 km per hour speed and the rest at 60 km per hour speed. How many hours did he travel at 60 km per hour?

OPtion

1) 4 hours 30 minutes
2) 3 hours 45 minutes
3) 5 hours 30 minutes
4) 4 hours 15 minutes
5) 3 hours 30 minutes
6) 5 hour 45 minutes
7) 8 hours
8) 9 hours
9) 7 hours
10) None of the above

Solution

Let Mohit travel 'x' hours at 50 km per hour.
As the total time taken to cover 720 km is 13.5 hours, he would have traveled (13.5-x) hours at 60 km per hour.
Distance covered at 50 km per hour = 50x km.
Distance covered at 60 km per hour = 60*(13.5-x) = 810 - 60x km.
Total distance covered = Distance covered at 50 km per hour + Distance covered at 60 km per hour.
720 = 50x + 810 - 60x
10x = 90
x = 9
Hence, the time for which he travel at 60 km/hr = 13.5 - 9 = 4.5 hours = 4 hours 30 minutes.

Correct Option: 1 Best Solution (1)

Varun   2 years AGO

speed s = distance d / time t
=> d = s*t
Total d = 720, part of t which is at 60kmph = x, rest = 13.5-x
=> 50(13.5-x) + 60x = 720
=> x = 4.5 = 4 hours and 30 minutes

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