Formula:
Lt + Lp = Speed of the Train × Time taken to cross the Platform
⇒ Length of Train = Lt
⇒ Length of Platform = Lp
Calculation:
Statement I:
Length of the Train A = Lt = 100 m
Length of the Platform (Lp) = 2 × Lt = 2 × 100 = 200 m
Speed of Train A = Sta
Time Taken to Cross the platform = 10 Sec
Lt + Lp = Speed of the Train × Time taken to cross the Platform
Lt + 2 × Lt = Sta × 10
100 + 200 = Sta × 10
300 = Sta × 10
Sta = 30 m/s
Time Taken by Train B = 20 s
Length of the Platform = 200 m
Length of the train B = Lb
Speed of Train B = Sb
Lb + Lp = Speed of the Train × Time taken to cross the Platform
Lt + 200 = Sb × 20
Length of the Train B is not given neither speed is given two variable needs two equation.
Statement II:
Speed of Train A = Sa
Speed of Train B = Sb
Sum of the speed of Train A and B is 200 m/s
Sa + Sb = 200 m/s ----(i)
Difference between the speed of Train A and Train B is 50 m/s
Sa – Sb = 50 m/s ----(ii)
Dividing (i) and (ii)
Using Componendo and Dividendo
Sa : Sb = 5 : 3
∴ The statement II alone is sufficient to answer the question, but the statement I alone is not sufficient.