Final answer:
To determine the time it took for a runner to complete a race, divide the race distance (421 meters) by the average velocity (5.42 m/s), resulting in approximately 77.68 seconds.
Step-by-step explanation:
To calculate how long it took the runner to complete a 4.21×10⁴ m race with an average velocity of 5.42 m/s, we can use the formula for time which is time = distance/velocity. The distance given is 4.21×10⁴ meters (which is 421 meters if we assume the missing exponent noted as a typo is 2 making it 10²), and the average velocity is 5.42 m/s.
Using the formula:
Time = Distance / Velocity
Time = 421 m / 5.42 m/s
Time ≈ 77.68 s
So, it took the runner approximately 77.68 seconds to complete the race.