To find out how many cups of almonds Luis needs when using 3 cups of chocolate chips, we can set up a proportion based on the recipe.
The recipe states that for every \( \frac{3}{4} \) cup of chocolate chips, \( \frac{1}{8} \) cup of almonds is needed.
First, we find how many times \( \frac{3}{4} \) fits into 3 cups of chocolate chips:
\[ \text{Number of times } \frac{3}{4} \text{ fits into } 3 = \frac{3}{\frac{3}{4}} = 3 \times \frac{4}{3} = 4 \]
This means Luis is using 4 times the amount of chocolate chips as in the recipe.
Now, we find out how many cups of almonds are needed, considering the recipe uses \( \frac{1}{8} \) cup of almonds for every \( \frac{3}{4} \) cup of chocolate chips:
\[ \text{Amount of almonds needed} = 4 \times \frac{1}{8} = \frac{4}{8} = \frac{1}{2} \text{ cup} \]
Therefore, Luis will need \( 0.5 \) cup of almonds.
Answer: 0.5 cup.