Problems & Solutions (Question/Answer)

[jai_bhardwaj]

Here are few questions and their answers ...............

[jai_bhardwaj]

A train running at the speed of 60 km/hr crosses a pole in 9 seconds. What is the length of the train?

A. 120 metres
B. 180 metres
C. 324 metres
D. 150 metres

Answer & Explanation

Answer: Option D

Explanation:

Speed= 60 x (5/18) m/sec = 50/3 m/sec.

Length of the train = (Speed x Time) = (50/3) x 9 m = 150 m.

[jai_bhardwaj]

A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:

A. 45 km/hr B. 50 km/hr
C. 54 km/hr D. 55 km/hr
Answer & Explanation
Answer: Option B

Explanation:

Speed of the train relative to man = 125/10 m/sec

= 25/2 m/sec.

= (25/2) x (18/5) km/hr

= 45 km/hr.

Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.

x - 5 = 45 x = 50 km/hr.

[jai_bhardwaj]

The length of the bridge, which a train 130 metres long and travelling at 45 km/hr can cross in 30 seconds, is:

A. 200 m B. 225 m
C. 245 m D. 250 m

Answer & Explanation

Answer: Option C

Explanation:

Speed = 45 x (5/18) m/sec = 25/2 m/sec.

Time = 30 sec.

Let the length of bridge be x metres.

Then, (130 + x)/30 = (25/2)

2(130 + x) = 750

x = 245 m.

[jai_bhardwaj]

Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. The ratio of their speeds is:

A. 1 : 3 B. 3 : 2
C. 3 : 4 D. None of these

Answer & Explanation

Answer: Option B

Explanation:

Let the speeds of the two trains be x m/sec and y m/sec respectively.

Then, length of the first train = 27x metres,

and length of the second train = 17y metres.

(27x + 17y)/(x+ y) = 23

27x + 17y = 23x + 23y

4x = 6y

x/y = 3/2 .

[jai_bhardwaj]

A train passes a station platform in 36 seconds and a man standing on the platform in 20 seconds. If the speed of the train is 54 km/hr, what is the length of the platform?

A. 120 m B. 240 m
C. 300 m D. None of these

Answer & Explanation

Answer: Option B

Explanation:

Speed = 54 x (5/18) m/sec = 15 m/sec.

Length of the train = (15 x 20)m = 300 m.

Let the length of the platform be x metres.

Then,( x + 300)/36 = 15

x + 300 = 540

x = 240 m.

[rajnish manga]

बहुत अच्छा आयोजन है, जय जी. हार्दिक धन्यवाद. गणितीय प्रश्नोत्तर (तर्क व हल समेत) का यह सूत्र खूब लोकप्रिय होगा, ऐसा मेरा विश्वास है.

[bindujain]

भारद्वाज जी सबलो का सिलसिला यदि हिंदी में हो तो बेहतर होगा