Sorry i didnot give you all the information the problem is U={a,b,c,d,e,f,g,h,i,j,k} A={a,c,d,f,g,i} B={b,c,d,f,g} C={a,b,f,i,,j}    question  (A n C)'

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(A u C) would refer to the union of A and C - and not the intersection. The intersection of A and C (A n C) would be all the points in A, and all the points in C, that are the same. (for example - if A contained the # 4 - and C contained the # 4 - then that would be an intersection)  'u' denotes union. (That's an easy way to remember it :D )  In this problem - the intersection of A and C (A n C) is {a, f, i} The union of A and C (A u C) is {a, b, c, d, f, g, i, j} [When you're talking about the union - you don't repeat values - I didn't write a, f, or i twice.] I hope I made sense through this...if not please let me know. :D  Good luck