Question

The time taken by train A is 3 hours more than the time taken by train B to cover a distance of 108 km. Find the speed of train B, if the speed of train B is 6 km/h more than train A. 
1. 18 
2. 24 
3. 30 
4. 36 

Answer 1

Correct Answer - Option 1 : 18 

Given :

The time taken by train A is 3 hours more than the time taken by train B to cover a distance of 108 km.

speed of train A is 6 km/h more than that of train B. 

Formula used :

Time = Distance/Speed 

Calculations :

Let the speed of train A be 'S' km/h 

So, the speed of train B will be 'S + 6' km/h 

let the time taken by train to cover the distance be 't' 

According to the question 

108/S = t      ....(1) 

108/(S + 6) = t - 3      ....(2) 

Subtracting equation (2) from (1) 

108/S - 108/(S + 6) = 3 

S² + 6S = 216 

⇒ S² + 6S - 216 = 0 

⇒ S² + 18S - 12S - 216 = 0 

⇒ S(S + 18) - 12(S + 18) = 0 

⇒ S = 12 and -18 

So speed of A = 12 km/h and speed of B = 12 + 6 = 18 km/h 

∴ The speed of the train B is 18 km/h