To determine the probability that a randomly selected student earned a grade of C or better, we need to sum the probabilities of receiving grades A, B, and C. These grades correspond to the numerical values 4, 3, and 2, respectively.
Given the probabilities:
- Probability of getting an A (4): [tex]\(0.43\)[/tex]
- Probability of getting a B (3): [tex]\(0.31\)[/tex]
- Probability of getting a C (2): [tex]\(0.17\)[/tex]
We sum these probabilities to find the probability of earning a C or better:
[tex]\[
\text{Probability of earning a C or better} = \text{Probability of A} + \text{Probability of B} + \text{Probability of C}
\][/tex]
[tex]\[
\text{Probability of earning a C or better} = 0.43 + 0.31 + 0.17
\][/tex]
Adding these values together:
[tex]\[
0.43 + 0.31 = 0.74
\][/tex]
[tex]\[
0.74 + 0.17 = 0.91
\][/tex]
Therefore, the probability that a randomly selected student earned a grade of C or better is [tex]\(0.91\)[/tex].
The correct answer is:
[tex]\[ \boxed{0.91} \][/tex]
