To determine the probability of randomly selecting a chocolate chip cookie, you divide the number of chocolate chip cookies by the total number of cookies:

$\text{Probability} = \frac{\text{Number of chocolate chip cookies}}{\text{Total number of cookies}} = \frac{8}{20} = 0.4$

This can also be expressed as 40%.

So, the correct answers are:

• 0.4
• 40%

The option "0.8" is incorrect because it would represent a situation where there are 16 chocolate chip cookies out of 20, not 8.

Would you like further clarification or examples? Here are a few related questions:

1. How would the probability change if there were 12 chocolate chip cookies out of 20 total cookies?
2. What is the probability of choosing a non-chocolate chip cookie?
3. How would the probability change if there were 8 chocolate chip cookies out of 50 total cookies?
4. What is the decimal form of a 30% probability?
5. If there are 5 chocolate chip cookies and 15 oatmeal cookies, what is the probability of choosing a chocolate chip cookie?

Tip: To convert a percentage to a decimal, simply divide by 100.