Answer:
2,000 seconds
Explanation:
A factory uses a water tank to cool one of its pieces of machinery. To keep the water cold, fresh water enters the tank at a rate of 4 kilograms per second. Water also flows out of the tank at the same rate. The tank holds 8,000 kilograms of water. The residence time for the average water molecule in that water tank is . 4 kilograms will go in the tank in 1 second. So for 8,000 kilograms of water you divide 8,000 by 4. Which gives you 2,000.
