Correct Answer - Option 2 :
\(\frac{4}{3} hours\)
Given:
Speed of X, Y and Z = 4 km/h, 5 km/h and 6 km/h.
Formula used:
Distance = Speed × Time
The relative speed of Y with respect to X = (Sx - Sy)
Where Sx and Sy are the speed of X and Y respectively.
Calculation:
Distance covered by X in 2 hours = 4 × 2
⇒ Distance covered by X in 2 hours = 8 km
Time required for Y to cover this distance = 8/(5 - 4)
⇒ Time required for Y to cover this distance = 8 hours
Let Z starts t hours after Y.
According to the question,
8 × 5 = (8 - t) × 6
⇒ 40 = 48 - 6t
⇒ 6t = 8
⇒ t = 4/3
∴ Z starts travelling 4/3 hours after Y.