To find the cost of 1 kilogram of avocados, we need to use the given ratio from the double number line.

The ratio given is:

$5 \text{ kilograms} = 9 \text{ dollars}$

Now, we want to find the cost for 1 kilogram. To do this, divide both sides of the ratio by 5:

$\frac{5 \text{ kilograms}}{5} = \frac{9 \text{ dollars}}{5}$

This simplifies to:

$1 \text{ kilogram} = \frac{9}{5} \text{ dollars}$

Performing the division:

$1 \text{ kilogram} = 1.8 \text{ dollars}$

Thus, the cost for 1 kilogram of avocados is $1.80.

Would you like further details or have any questions?

Here are some related questions:

1. What would the cost be for 10 kilograms of avocados?
2. How would you find the cost for 2.5 kilograms using the same ratio?
3. What is the unit rate in dollars per kilogram, and why is it important?
4. Can you express the price as a fraction of dollars per kilogram?
5. How does changing the amount of avocados affect the total cost?

Tip: When dealing with ratios, always reduce to the unit rate (per 1 unit) to simplify calculations.