CDS Model Paper 5 Mathematics

Let the speed of train be x‌km∕h and actual time taken is t hrs.
In first case, distance =(x+6)(t−4)‌km ...(i)
In second case, distance =(x−6)(t+6)‌km ...(ii)
Also distance =xt from (i) and (ii)
(x+6)(t−4)=(x−6)(t+6) ...(iii)
⇒

x+6

x−6

=

t+6

t−4

⇒

x

6

=

2t+2

10

⇒

x

6

=

t+1

5

⇒ 5x=6t+6⇒5x−6t=6
⇒ t=

5x−6

6

Putting the value of 't' in eqn. (iii), we get
x=30‌km∕hr
∴ t=24‌hr
Thus, distance =30×24=720