The problem tells us that the number of pages $p$ Deandre reads is proportional to the time $t$ he spends reading. This suggests a proportional relationship of the form:

$p = k \cdot t$ where $k$ is the constant of proportionality. To find $k$, we can use the information that Deandre reads 24 pages in 40 minutes:

$24 = k \cdot 40$

Solving for $k$:

$k = \frac{24}{40} = 0.6$

Thus, the equation that represents this proportional relationship is:

$p = 0.6 \cdot t$

The correct answer is D: $p = 0.6t$.

Would you like further clarification on this problem or any other questions? Here are some related topics:

1. How to solve problems involving direct proportionality.
2. How to use the constant of proportionality to predict values.
3. What happens when the relationship is inverse instead of direct.
4. How to graph proportional relationships.
5. How to find the constant of proportionality from given data.

Tip: Whenever you encounter a proportionality problem, always remember to first find the constant of proportionality (k) by using known values.