A practical problem states that a car travels 60 km/h and a truck travels 40 km/h. If they start from the same point and the car is 30 minutes ahead, how far will they be from the starting point when they meet?
Answer: B. 90 km
Let t be the time in hours after the car started. The car travels 60t and the truck travels 40(t - 0.5). Setting these equal gives 60t = 40(t - 0.5), solving gives t = 1.5 hours, thus the distance is 60 * 1.5 = 90 km.