A car climbs a mountain path 12 km long at 4 km/h and descends the same distance at 12 km/h. Find the average speed for the round journey. MCQ with Answer and Explanation

Explanation:
Speed of train = 36 * (5/18) = 10 m/s. Length of train = Speed * Time to cross post = 10 * 6 = 60 meters. Total distance to cross platform = Speed * Time = 10 * 12 = 120 meters. Platform length = 120 - 60 = 60 meters.

Explanation:
Time difference = 5 - (-5) = 10 minutes = 1/6 hour. Let distance be d. d/12 - d/15 = 1/6 => (5d - 4d)/60 = 1/6 => d/60 = 1/6 => d = 10 km.

Explanation:
Total path distance = 140 + 110 = 250 meters. Relative speed index in same direction = 52 - 42 = 10 km/h = 10 * (5/18) = 25/9 m/s. Time required = 250 / (25/9) = 250 * 9 / 25 = 10 * 9 = 90 seconds.