386. A train runs from Howrah to Bandel at an average speed of 20 km/hr and returns at an average speed of 30 km/hr. The average speed (in km/hr) of the train in the whole journey is

1. 1. 20

   
   
   

   2. 22.5

   
   
   

   3. 24

   
   
   

   4. 25

   
   
   

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1. View Hint View Answer Discuss in Forum

   Average speed =	2xy	kmph
   	x + y

   
   

   =	2 × 20 × 30
   	20 + 30

   
   

   =	2 × 20 × 30	= 24 kmph
   	50

   Correct Option: C

   Average speed =	2xy	kmph
   	x + y

   
   

   =	2 × 20 × 30
   	20 + 30

   
   

   =	2 × 20 × 30	= 24 kmph
   	50

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387. A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is

1. 1. 37.5

   
   
   

   2. 37

   
   
   

   3. 35

   
   
   

   4. 40

   
   
   

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1. View Hint View Answer Discuss in Forum

   Average speed of whole journey =		2xy		kmph
   		x + y

   
   

   =	2 × 50 × 30	kmph
   	50 + 30

   
   

   =	2 × 50 × 30	= 37.5 kmph
   	80

   Correct Option: A

   Average speed of whole journey =		2xy		kmph
   		x + y

   
   

   =	2 × 50 × 30	kmph
   	50 + 30

   
   

   =	2 × 50 × 30	= 37.5 kmph
   	80

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388. A man walks from his house at an average speed of 5 km per hour and reaches his office 6 minutes late. If he walks at an average speed of 6 km/h he reaches 2 minutes early. The distance of the office from his house is

1. 1. 6 km

   
   
   

   2. 9 km

   
   
   

   3. 12 km

   
   
   

   4. 4 km

   
   
   

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1. View Hint View Answer Discuss in Forum

   Required distance of office from house = x km. (let)
   

   Time =	Distance
   	Speed

   
   ∴  According to the question,
   

   x	−	x	=	6 + 2	=	2
   5		6		60		15

   
   

   ⇒	6x − 5x
   	30

   
   

   =	2
   	15

   
   

   ⇒	x	=	2
   	30		15

   
   

   ⇒ x =	2	× 30 = 4 km.
   	15

   
   
   Second Method :
   Here, S₁ = 5, t₁ = 6
   S₂ = 6, t₂ = 2
   

   Distance =	(S1 × S2)(t1 + t2)
   	S2 − S1

   
   

   =	(5 × 6)(6 + 2)
   	6 − 5

   
   

   = 30 ×	8	= 4 km.
   	60

   Correct Option: D

   Required distance of office from house = x km. (let)
   

   Time =	Distance
   	Speed

   
   ∴  According to the question,
   

   x	−	x	=	6 + 2	=	2
   5		6		60		15

   
   

   ⇒	6x − 5x
   	30

   
   

   =	2
   	15

   
   

   ⇒	x	=	2
   	30		15

   
   

   ⇒ x =	2	× 30 = 4 km.
   	15

   
   
   Second Method :
   Here, S₁ = 5, t₁ = 6
   S₂ = 6, t₂ = 2
   

   Distance =	(S1 × S2)(t1 + t2)
   	S2 − S1

   
   

   =	(5 × 6)(6 + 2)
   	6 − 5

   
   

   = 30 ×	8	= 4 km.
   	60

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389. A train runs at an average speed of 75 km/hr. If the distance to be covered is 1050 kms, how long will the train take to cover it ?

1. 1. 13 hrs

   
   
   

   2. 12 hrs

   
   
   

   3. 15 hrs

   
   
   

   4. 14 hrs

   
   
   

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1. View Hint View Answer Discuss in Forum

   Time =	Distance
   	Speed

   
   

   =	1050	= 14 hours
   	75

   Correct Option: D

   Time =	Distance
   	Speed

   
   

   =	1050	= 14 hours
   	75

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390. A train travels 500 m in first minute. In the next 4 minutes, it travels in each minute 125 m more than that in the previous minute. The average speed per hour of the train during those 5 minutes will be

1. 1. 30 km/hr

   
   
   

   2. 45 km/hr

   
   
   

   3. 50 km/hr

   
   
   

   4. 55 km/hr

   
   
   

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1. View Hint View Answer Discuss in Forum

   Total distance covered by train in 5 minutes
   = (500 + 625 + 750 + 875 + 1000) metre = 3750 metre
   = 3.75 km.
   

   Time = 5 minutes =	5	hour
   	60

   
   

   =	1	hour
   	12

   
   

   Speed of train =	Distance
   	Time

   
   

   =		3.75		kmph
   		(1/12)

   
   = (3.75 × 12) kmph
   = 45 kmph

   Correct Option: B

   Total distance covered by train in 5 minutes
   = (500 + 625 + 750 + 875 + 1000) metre = 3750 metre
   = 3.75 km.
   

   Time = 5 minutes =	5	hour
   	60

   
   

   =	1	hour
   	12

   
   

   Speed of train =	Distance
   	Time

   
   

   =		3.75		kmph
   		(1/12)

   
   = (3.75 × 12) kmph
   = 45 kmph

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