Ratio of red squares to green diamonds in a grid.

Let's solve the problem step by step.

We are given an image with red squares (■) and green diamonds (◆), and we are asked to find the ratio of red squares to green diamonds.

Step 1: Count the red squares (■)

Looking at the image:

- There are 5 rows of red squares.
- Each row has 4 red squares.

So, total red squares =
$$
5 \times 4 = 20
$$

Step 2: Count the green diamonds (◆)

Now look at the green diamonds:

- There are 5 rows of green diamonds.
- Each row has 5 green diamonds.

So, total green diamonds =
$$
5 \times 5 = 25
$$

Step 3: Write the ratio of red to green

We want the ratio of red squares to green diamonds:

$$
\text{Ratio} = \frac{\text{Red}}{\text{Green}} = \frac{20}{25}
$$

Simplify the fraction:

$$
\frac{20}{25} = \frac{4}{5}
$$

Final Answer:

$$
\boxed{4:5}
$$

So, the ratio of red squares to green diamonds is 4:5.