the temperature of the pool water started at 82 degrees, and it cooling down at 4.0 degrees each hour. If the water temperature is now 78 degrees, then how many hours have passed?

In general, the most common pool temperature for a residential pool used for leisure is between 78°F and 82°F (26°C and 28°C). But it's important to know that some temperatures can be dangerous for certain at-risk groups of people, and can make your pool vulnerable to contaminants i would say about 5 to 10 hrs