Final answer:
The joint probability density function for the two test scores, writing test score (x) and critical thinking test score (y), is given by Ρ(x, y) = {x + y if 0 <= x <= 1 and 0 <= y <= 1, 0 otherwise}.
Step-by-step explanation:
The joint probability density function for the two test scores, writing test score (x) and critical thinking test score (y), is given by:
Ρ(x, y) = {x + y if 0 <= x <= 1 and 0 <= y <= 1, 0 otherwise}
This means that the probability of a score (x, y) is equal to the sum of x and y, within the range of 0 to 1 for both x and y. Outside of this range, the probability is 0.