Two goods trains A and B are running on the same track but in opposite directions. A starts from P and B starts from Q towards each other. P and Q are 250 km apart. A travels 20 km/h and the speed of B is half that of A. What will be the distance between the two trains a minute before the collision?

The speed of train B is half of 20 km/h, which is 10 km/h. Using the relative speed concept for objects moving in opposite directions, their combined speed is 20 + 10 = 30 km/h, which converts to 30 / 60 = 0.5 km per minute. Therefore, the distance between them exactly one minute before collision is 1 * 0.5 = 0.5 km.

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