Question

{(1,2), (3,5)} is a partition of {1,2,3,4,5}?

Answer 1

A partition of the set A is the set of subsets of A, such that it doens't contain an empty set, their unification is equal to A and the intersection of any two elements is an empty set.

$(1,2) ∪(3,5)=(1,2,3,5)\not=(1,2,3,4,5)$ . So, {(1,2), (3,5)} is not a partition of {1,2,3,4,5}