Ratio: Identifying and defining elements

The total volume of water that fills the tank is $20$ liters over $5$ minutes. The flow rate is given by the volume divided by time:
$\text{Flow Rate} = \frac{\text{Total Volume}}{\text{Time}} = \frac{20}{5} = 4$
Thus, the water flows at a rate of $4$ liters per minute.

To solve this problem, we'll follow these steps:

• Step 1: Identify the total number of oranges that grow, which is 8.
• Step 2: Note the total number of days in which the 8 oranges grow, which is 4 days.
• Step 3: Apply the formula for the growth rate: $\text{Growth rate} = \frac{\text{Total number of oranges}}{\text{Total number of days}}$.
• Step 4: Calculate the growth rate by dividing 8 by 4.

Now, let's work through each step:
Step 1: The problem gives us a total of 8 oranges.
Step 2: These oranges grow over a period of 4 days.
Step 3: Using the formula, we find the growth rate: $\frac{8}{4} = 2$ oranges per day.

Therefore, the solution is that the growth rate is 2 oranges per day.