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A car and a bus start at 8:00 am from the same point and travel in the same direction. The average speed of the car is 60 mph.
In 2 hours the car is 30 miles ahead of the bus. Find the average speed of the bus.
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In 2 hours the car traveled 2*60 = 120 miles.
At that time the bus was 30 miles behind the car. Hence, the bus covered only 120-30 = 90 miles in 2 hours.
Hence, the bus' average speed was = 45 miles per hour.
The problem is solved in 3 (three) lines and without any equations.
You only need to think.