Question 1035036
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Let me introduce more convenient notation.


Let |A| be the number of elements of the set A;
    |B| be the number of elements of the set B;
    |C| be the number of elements of the set C.

Let AB be the intersection of A and B;
    AC be the intersection of A and C;
    BC be the intersection of B and C.

Let |AB| be the number of elements in AB;
    |AC| be the number of elements in AC;
    |BC| be the number of elements in BC.

Let ABC be the intersection of the sets A, B, and C, and
    |ABC| be the number of elements in ABC.

Then there is a remarkable formula:

n(A U B U C) = |A| + |B| + |C| - |AB| - |AC| - |BC| + |ABC|.

For its proof see the lesson <A HREF=https://www.algebra.com/algebra/homework/word/misc/Advanced-probs-counting-elements-in-sub-sets-of-a-given-finite-set.lesson>Advanced problems on counting elements in sub-sets of a given finite set</A> in this site.

Now apply the formula. You have everything to calculate the right side. It is 

30 + 32 + 31 - 16 - 19 - 18 + 8 = 48.

<U>Answer</U>. n(A U B U C) = 48.
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