Given n(A) = 1400, n(A ∪ B) = 2280, and n(A ∩ B) = 350, find n(B).

Question

what does the U up and U down mean?

Answer 1

The U up means union, everything in both sets, but listed only once.

 

{1,2,3,4} U {3,4,5} = {1,2,3,4,5}

 

The upside down is intersection. The intersection of the same two sets would be {3,4}.