A pair, is 2. A pair of anything, is 2 of them. Yes, it can be evaluated as 2 * x, but the value must remain so the meaning is different.
Situation: You have apples to divide among people. You have 6 apples. A family (f) is 2 adults and 1 child, so f = 2+1

6 apples divided by a pair of families (where there are 3 in a family). f is a family of 3, so f = 3
6 ÷ 2f = 6 ÷ 2(3) = 1
6 ÷ 2(2+1) = 1