Marking papers is a very hard thing, and it is not necessarily the front-line teacher who marks your papers. Therefore, grading is generally based on the answer, which is different from the answer. If the judges don't look carefully, you won't score.
Just like the calculation problem in the example, if your calculation result is correct, you may be judged to be correct. If your calculation result is wrong and the process is different from the "correct answer", you are likely to get cold. Prove that the problem is even more so. . .