Consider two groups
A = {1,w,w²}, Identity element =1
And, B= {1,-1}Identity element =1
Both are forming groups with respect to multiplication.
The first group A has 3 elements and the second group B has 2 elements.
Do, you think can we add them.
How will you add them, there are three elements in group A and 2 elements in group B, giving no benefit.
No, we can't add them.