Final answer:
The statement lacks the distance between the two cities, which is essential for calculating the biker's speed and subsequent distance covered in a given period, such as half the total time.
Step-by-step explanation:
The statement "It took 4 hours for a biker to travel at a certain speed from one city to another" is missing a crucial piece of information to determine other related quantities: the distance between the two cities. Without the distance, one cannot calculate the biker's speed, nor can we determine at what time the motorcycle had covered half the total distance or what distance the motorcycle had covered in half the total time.
In problems like this, knowledge of the distance, as well as the time taken to travel it, is vital in order to calculate the speed. Speed is defined as the distance traveled divided by the time taken to travel that distance. Once the speed is known, one can then find out how far the biker rode within a certain portion of the time, such as half. For example, if we knew that the biker traveled 100 kilometers in those 4 hours, we could determine that the biker's speed was 25 kilometers per hour. This would mean that in 2 hours (half the total time), the biker would have covered 50 kilometers.