But if I put 4 and 5 will I be wrong

The question asks for the probability that the sum of two numbers is at least 8. A probability is a value between 0 and 1, usually expressed as a fraction, decimal, or percentage.

While $(4,5)$ is one of the pairs whose sum is at least 8, and 4 and 5 are numbers involved in the calculation, they do not represent the probability itself. The probability is the ratio of favorable outcomes to total outcomes, which we calculated as $\frac{3}{9}$ or $\frac{1}{3}$.