Final answer:
The rate of change of the water level in the swimming pool is 10 gallons per hour.
Step-by-step explanation:
The rate of change of the water level in the swimming pool can be calculated by dividing the rate at which the pool is being drained by the time it takes to drain the pool. In this case, the pool is being drained at a rate of 50 gallons per hour. Since the pool contains 500 gallons, it would take 500 / 50 = 10 hours to completely drain the pool. Therefore, the rate of change of the water level in the swimming pool is 10 gallons per hour.