To travel 612 km, Train A takes 9 hours more than Train B. If the speed of the Train A is doubled, it takes 3 hours less than Train B. The speed (in km/h) of Train B is:
Answer & explanation
Correct answer: option 3
Let us consider that ,
Speed of B = s km/h
We know that ,
Time = \(\frac{Distance}{Speed}\)
Time taken by B = \(\frac{612}{s}\)
Time taken by A = [ ( \(\frac{612}{s}\) ) + 9 ]
Speed of A = \(\frac{612}{ [ 612/s + 9 ]}\)
According to question ,
612 = 2 × \(\frac{612}{ [ 612/s + 9 ]}\) × [ \(\frac{612}{s}\) - 3 ]
612 = 2 × \(\frac{612}{ [ 612/s + 9 ]}\) × [ \(\frac{612}{s}\) - 3 ]
\(\frac{612}{s}\) + 9 = 2 × [ \(\frac{612}{s}\) - 3 ]
\(\frac{612}{s}\) + 9 = 2 × \(\frac{612}{s}\) - 6
\(\frac{612}{s}\) = 15
s = 40.8 km/h