How many liters of water are in a 21 foot round pool that is 4.5 feet deep?

To calculate the number of liters of water in a round pool, we need to determine the volume of the pool. The formula for the volume of a cylinder (which approximates the shape of a round pool) is:

```

V = πr²h

```

where:

- V is the volume in cubic units (cubic meters or cubic feet in this case)

- π is a mathematical constant approximately equal to 3.14

- r is the radius of the pool in the same units as h

- h is the height of the pool in the same units as r

In this case, the pool is 21 feet in diameter, so the radius is half of that, or 10.5 feet. The pool is 4.5 feet deep.

First, we need to convert the measurements to the same unit. We will use feet for this example:

```

r = 10.5 feet

h = 4.5 feet

```

Now we can plug these values into the formula:

```

V = π(10.5 feet)²(4.5 feet)

```

```

V ≈ 3.14 x 110.25 x 4.5

```

```

V ≈ 1520.625 cubic feet

```

To convert cubic feet to liters, we can use the conversion factor 1 cubic foot = 28.3168 liters:

```

V = 1520.625 cubic feet x 28.3168 liters / cubic foot

```

```

V ≈ 43008 liters

```

Therefore, the 21-foot round pool with a depth of 4.5 feet holds approximately 43,008 liters of water.