Refer to a specific value in a cell

I'm fairly new to databases so forgive me my silly question.

I want to refer to a specific value in a cell in another table and use this value in a mathematical function (e.g. mutiply or divide it). 
For example:

I have two tables, table A and B.
In table A, I have student performances in an exam (eg. each row for one student and his/her points; task 1= 20 point, task 3= 30 points etc.)
In table B, I have the tasks of the exams and their maximum number of points (e.g. task 1=30 points, task 2=60 points).
Now I want to add to table A the following. After each points column (including the number reached by the student), I want to have the percentage of how well he/she has done (e.g. task 1: 66%, task 2: 50%).
I tried working with table relationships and formulars, but I don't know how to divide a value from one table by a specific value from another table. I know how this works in Excel, but I haven't firgured out a way to do this in a database.

I hope I could present my problem understandably. If not, please tell me so I can be more detailed. TIA :)

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