A train , 800 meter long is running with a speed of 78 km/hr. It crosses a tunnel in 1 minute. What is the length of the tunnel (in meters)?  Select:  A) 440 m  B) 500 m  C) 260 m  D) 430 m  E) 450 m

Rationale: "explanation : distance = 800 + x meter where x is the length of the tunnel time = 1 minute = 60 seconds speed = 78 km / hr = 78 × 10 / 36 m / s = 130 / 6 = 65 / 3 m / s distance / time = speed ( 800 + x ) / 60 = 65 / 3 = > 800 + x = 20 × 65 = 1300 = > x = 1300 - 800 = 500 meter answer : option b"
Answer: B