# Aptitude - Problems on Trains - Discussion

Discussion Forum : Problems on Trains - General Questions (Q.No. 2)

2.

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:

Answer: Option

Explanation:

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

10 |

= | 25 | m/sec. | |

2 |

= | 25 | x | 18 | km/hr | |

2 | 5 |

= 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.

Discussion:

461 comments Page 1 of 47.
Neha Kumari said:
2 weeks ago

How answer is 50 km/hr? Please explain to me.

(3)

Moustafa Elhosiny said:
2 months ago

Sp of man = 5 * 5/18

= 25/18 m/sec.

Let Sp of train be x, then;

x - 25/18 = 125/10

So x = 125/10 + 25/18 = 125/9 m/sec.

So x = 125/9 * 18/5 =50 Km/h.

= 25/18 m/sec.

Let Sp of train be x, then;

x - 25/18 = 125/10

So x = 125/10 + 25/18 = 125/9 m/sec.

So x = 125/9 * 18/5 =50 Km/h.

(29)

Santhosh K said:
3 months ago

@All.

Why do we minus the speed of the man moving in the same direction? Please explain to me.

Why do we minus the speed of the man moving in the same direction? Please explain to me.

(30)

SoloStriver said:
3 months ago

Consider we need to convert m/sec to km/hr..

If we need to convert something from m to km, 1km=1000m. Thus 1m= (1/1000)km

So we multiply the numerator by 1/1000.

Similarly, (denominator part) for a sec to hr, 1hr=3600sec. Thus 1sec=(1/3600)hr.

So we multiply the denominator by 1/3600.

This conversion part becomes 3600/1000 thus simplifying this gives an std form of 18/5.. which is always directly used in converting m/sec conversion to km/hr.. helps in just multiplying this 18/5, instead of separate conversion of numerator and denominator to km and hr separately which is time-consuming..

Similarly, the reciprocal of this is just the vice versa case from km/hr to m/sec just multiply with 5/18.

If we need to convert something from m to km, 1km=1000m. Thus 1m= (1/1000)km

So we multiply the numerator by 1/1000.

Similarly, (denominator part) for a sec to hr, 1hr=3600sec. Thus 1sec=(1/3600)hr.

So we multiply the denominator by 1/3600.

This conversion part becomes 3600/1000 thus simplifying this gives an std form of 18/5.. which is always directly used in converting m/sec conversion to km/hr.. helps in just multiplying this 18/5, instead of separate conversion of numerator and denominator to km and hr separately which is time-consuming..

Similarly, the reciprocal of this is just the vice versa case from km/hr to m/sec just multiply with 5/18.

(22)

Ravina Sonawane said:
4 months ago

According to me, it should be 25/2 × 18/5 = 45.

(39)

Bandi Pravalika said:
5 months ago

18/5 is the direct formula to convert the m/seconds to km/hr.

In this given problem, we can convert the m/sec to km/hr so we use 18/5.

In this given problem, we can convert the m/sec to km/hr so we use 18/5.

(14)

Murugan S said:
5 months ago

HERE,

1hr = 3600sec then, 1sec = 1/3600hr

1km =1000m then, 1m = 1/1000km

So,

km/hr to m/s is : 1/1000km bigger divided by 1/3600hr.

So, they put 18/5.

1hr = 3600sec then, 1sec = 1/3600hr

1km =1000m then, 1m = 1/1000km

So,

km/hr to m/s is : 1/1000km bigger divided by 1/3600hr.

So, they put 18/5.

(19)

Fizza akhtar said:
5 months ago

Suppose we have to convert km/hour into m/s.

km/hour = 1000m/hour

i hour = 3600s

km/s = 1000m/3600s = 5/18.

Just reverse it, m/s into km/hour = 18/5, it's an easy way.

km/hour = 1000m/hour

i hour = 3600s

km/s = 1000m/3600s = 5/18.

Just reverse it, m/s into km/hour = 18/5, it's an easy way.

(9)

MAHA said:
8 months ago

How 18/5? Please explain to me.

(51)

Adesh Katiya said:
8 months ago

l = 125m,

u = 5km/hr,

v = ?

t = 10s.

u - v = 125/10 m/s,

u - v = 25/2 m/s,

u - v = 5*9 km/hr,

u - v = 45km/hr,

5km/hr - v = 45km/hr.

v = 50 km/hr.

Hence, option (B).

u = 5km/hr,

v = ?

t = 10s.

u - v = 125/10 m/s,

u - v = 25/2 m/s,

u - v = 5*9 km/hr,

u - v = 45km/hr,

5km/hr - v = 45km/hr.

v = 50 km/hr.

Hence, option (B).

(46)

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