Creating an equation from a group of numbers and the answer

Question

sigh... I've been trying for three days to figure out this one last question. Any help will be much appreciated, thank you.

The objective is to create an equation/formula with the given information of the numbers it consists of and the answer.
The equation/formula must be applicable to all four groups of information.

No. 20 is the only other question with fractions so I added it as an example. No. 20's answer is the numerator(n) divided by the denominator(d) with the decimals removed.

Questions:

20. numbers answers

    1/3 - 0

    2/3 - 0

    3/3 - 1

    4/5 - 0

    equation n ÷ d = a, then remove decimals e.g.

    1 ÷ 3 = 0.3333333333 = 0
    2 ÷ 3 = 0.6666666667 = 0
    3 ÷ 3 = 1
    4 ÷ 5 = 0.8 = 0
    

21. numbers answers

    2/3, 5/5 - 2

    2/3, 4/5 - 0

    2/2, 2/3 - 3

    1/2, 3/3 - 2

    equation ?