A person walking at 4/5 of his usual speed reaches his office 10 minutes late. What is his usual time? MCQ with Answer and Explanation

Explanation:
Time difference = 15 - (-5) = 20 minutes = 20/60 = 1/3 hours. Let distance be d. d/5 - d/7.5 = 1/3 => (1.5d - d) / 7.5 = 1/3 => 0.5d / 7.5 = 1/3 => d / 15 = 1/3 => d = 5 km.

Explanation:
Relative speed = 300 / 25 = 12 m/s = 12 * (18/5) = 43.2 km/h. Since they move in opposite directions, Relative Speed = Speed of train + Speed of worker => 43.2 = Speed of train + 6 => Speed of train = 37.2 km/h.

Explanation:
New speed = 5/6 of usual speed => New time = 6/5 of usual time. Difference = 1/5 of usual time = 10 minutes. Typical baseline time = 10 * 5 = 50 minutes.