Why this answer (set unions)

[user44]

What if Set A = {1} and Set B = {1, 1}? Then the maximum possible number of elements that are in A∪B would be 1 only, which is NOT m+n? Since m+n would be 3 in my provided example?

I read m and n as the number of elements in the set, not the elements themselves?

Thanks

[Leaderboard]

@user44

Set B = {1, 1}

which is {1}.