Speed, Time and Distance
 A train moves with a speed of 30 kmph for 12 minutes and for next 8 minutes at a speed of 45 kmph. Find the average speed of the train:

 37.5 kmph
 36 kmph
 48 kmph
 30 kmph

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Average speed = Total distance time taken = 30 × 12 + 45 × 8 60 60 12 + 8 60 60
= 12 × 3 = 36 kmphCorrect Option: B
Average speed = Total distance time taken = 30 × 12 + 45 × 8 60 60 12 + 8 60 60
= 12 × 3 = 36 kmph
 A person travels 600 km by train at 80km/hr, 800 km by ship at 40 km/hr 500 km by aeroplane at 400 km/hr and 100 km by car at 50km/hr. What is the average speed for the entire distance ?


65 5 km./hr. 123  60 km./hr.

60 5 km./hr. 123  62 km./hr.


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Total time = 600 + 800 + 500 + 100 80 40 400 50 = 246 hours. 8 Average speed = 600 + 800 + 500 +100 246 8 = 2000 × 8 246 = 65 5 km/hr. 123 Correct Option: A
Total time = 600 + 800 + 500 + 100 80 40 400 50 = 246 hours. 8 Average speed = 600 + 800 + 500 +100 246 8 = 2000 × 8 246 = 65 5 km/hr. 123
 A boy rides his bicycle 10km at an average speed of 12 km/hr and again travels 12 km at an average speed of 10 km/hr. His average speed for the entire trip is approximately :

 10.4 km/hr
 10.8 km/hr
 11.0 km/hr
 12.2 km/hr

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Total distance = 10 + 12 = 22 km
Total time = 10 + 12 12 10 = 244 hours 120 ∴ Required average speed = Total distance Total time = 22 244 120 = 22 × 120 = 10.8 km/hr. 244
Second Method :
Here, d_{1} = 10, S_{1} = 12
d_{2} = 12, S_{2} = 10Average Speed = d_{1} + d_{2} d_{1} + d_{2} S_{1} S_{2} = 10 + 12 10 + 12 12 10 = 22 × 120 = 10.8 km/hrs. 244 Correct Option: B
Total distance = 10 + 12 = 22 km
Total time = 10 + 12 12 10 = 244 hours 120 ∴ Required average speed = Total distance Total time = 22 244 120 = 22 × 120 = 10.8 km/hr. 244
Second Method :
Here, d_{1} = 10, S_{1} = 12
d_{2} = 12, S_{2} = 10Average Speed = d_{1} + d_{2} d_{1} + d_{2} S_{1} S_{2} = 10 + 12 10 + 12 12 10 = 22 × 120 = 10.8 km/hrs. 244
 A car moving in the morning fog passes a man walking at 4 km/h. in the same direction. The man can see the car for 3 minutes and visibility is upto a distance of 130 m. The speed of the car is :


7 3 km. per hour 5 
6 3 km. per hour 5  7 km. per hour
 5 km. per hour


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Speed of car = x kmph.
Relative speed = (x – 4) kmph.Time = 3 minutes = 3 hours = 1 hours 60 20
Distance = 130 metre= 130 km. = 13 km. 1000 100 ∴ Relative speed = Distance Time ⇒ x – 4 = 13 × 20 100
⇒ 5x – 20 = 13
⇒ 5x = 20 + 13 = 33⇒ x = 33 = 6 3 kmph. 5 5 Correct Option: B
Speed of car = x kmph.
Relative speed = (x – 4) kmph.Time = 3 minutes = 3 hours = 1 hours 60 20
Distance = 130 metre= 130 km. = 13 km. 1000 100 ∴ Relative speed = Distance Time ⇒ x – 4 = 13 × 20 100
⇒ 5x – 20 = 13
⇒ 5x = 20 + 13 = 33⇒ x = 33 = 6 3 kmph. 5 5
 A car covers a certain distance in 25 hours.
less in that time. The speed of car isIf it reduces the speed by 1 th,the car covers 200 km. 5

 60 km./hr.
 30 km./hr.
 40 km./hr.
 50 km./hr.

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Speed of car = x kmph.
∴ Distance = Speed × Time
= 25x km.
Case II,Speed of car = 4x kmph. 5 Distance covered = 4x × 25 5
= 20x km.
According to the question,
25x – 20x = 200
⇒ 5x = 200⇒ x = 200 = 40 kmph. 5 Correct Option: C
Speed of car = x kmph.
∴ Distance = Speed × Time
= 25x km.
Case II,Speed of car = 4x kmph. 5 Distance covered = 4x × 25 5
= 20x km.
According to the question,
25x – 20x = 200
⇒ 5x = 200⇒ x = 200 = 40 kmph. 5