However, in some formal examinations and assessments, letters and data need to be marked with black pens. This is to ensure that the respondent's answer is clear and easy to read, and it is not easy to be modified or tampered with.
Generally speaking, it is a common practice to mark data with a pencil in primary school mathematics drawing problems. However, in some cases, you may need to use a black pen. What tools to use can be decided according to the requirements of teachers or exams.