A train covers a certain distance in one hour. If the speed of the train is increased by 10 km/hr, how long will it take to cover that distance?

This is a classic trick question. We know time = distance/speed. If the original time is 1 hour, distance = speed (let's call it s). New speed = s+10, so new time = s/(s+10) hours. Without knowing the original speed (or distance), we cannot determine the new time. For example: if s=50 km/h, time = 50/60 = 50 minutes; if s=100 km/h, time = 100/110 ≈ 54.5 minutes. The answer varies, so 'Cannot be determined' is correct.