Yes you can? Glad I taught my children math.
Math is one of the things they are not screwed up about.
The question is poorly worded, and therefore doesn't clearly state the point it is trying to address, which is that it is oftentimes easier to do sums in one's head if one can "convert" at least one or more of the addends to a multiple of ten. In other words, what the problem wants the student to do is to first decompose one of the addends into a sum of two separate addends, and then use the associative property of addition to simplify the problem.
The question presents a very simplified fact pattern for this exercise, which is why it might appear bizarro-world to those who just see the question.
The correct answer is as follows:
8 + 5 =
8 + (2 + 3) =
(8 + 2) + 3 =
10 + 3 =
13
It is the penultimate step that the question is aiming at.
A more complex version might be: find the sum of 17 + 5 + 18. By inspection, 5 decomposes into (3 + 2) and then application of the associative property converts the problem into the sum of (17 + 3) + (2 + 18) = 20 + 20 = 40.