Time and Distance

11. An aeroplane covers a certain distance at a speed of 240 kmph in 5 hours. To cover the same distance in 1 hours, it must travel at a speed of:

by
[A]. 300 kmph
[B]. 360 kmph
[C]. 600 kmph
[D]. 720 kmph
✅ The correct answer is option D.
Distance = (240 x 5) = 1200 km.
Speed = Distance/Time
Speed = 1200/(5/3) km/hr.     [We can write 1 hours as 5/3 hours]

Required speed =

1200 x
3
km/hr
= 720 km/hr.

5

12. It takes eight hours for a 600 km journey, if 120 km is done by train and the rest by car. It takes 20 minutes more, if 200 km is done by train and the rest by car. The ratio of the speed of the train to that of the cars is:

by
[A]. 2 : 3
[B]. 3 : 2
[C]. 3 : 4
[D]. 4 : 3
✅ The correct answer is option C.
Let the speed of the train be x km/hr and that of the car be y km/hr.

Then,
120
+
480
= 8      
1
+
4
=
1
….(i)

x
y
x
y
15

And,
200
+
400
=
25
   
1
+
2
=
1
….(ii)

x
y
3
x
y
24

Solving (i) and (ii), we get: x = 60 and y = 80.
Ratio of speeds = 60 : 80 = 3 : 4.

14. In a flight of 600 km, an aircraft was slowed down due to bad weather. Its average speed for the trip was reduced by 200 km/hr and the time of flight increased by 30 minutes. The duration of the flight is:

by
[A]. 1 hour
[B]. 2 hours
[C]. 3 hours
[D]. 4 hours
✅ The correct answer is option A.
Let the duration of the flight be x hours.

Then,
600
–
600
= 200

x
x + (1/2)

600
–
1200
= 200

x
2x + 1

x(2x + 1) = 3
2×2 + x – 3 = 0
(2x + 3)(x – 1) = 0
x = 1 hr.      [neglecting the -ve value of x]