Question 1072460
.
<pre>
The number of elements in the union A U B is

     n(A U B) = n(A) + n(B) - n(A n B),                  (*)

where (A n B) symbolizes the intersection of A and B.  By substituting the given data, you get

     132      =  80  + 75   - n(A n B),


It implies     n(A n B) = 80   +  75  - 132      = 155 - 132 = 23.


Thus you found out that the intersection  (A n B) contains 23 elements.


Therefore,   the number of elements that are in A, but not in B is 80 - 23 = 57.


<U>Answer</U>.  The number of elements that are in A, but not in B is  57.
</pre>

Regarding formula (*), see the lesson 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/word/misc/Counting-elements-in-sub-sets-of-a-given-finite-set.lesson>Counting elements in sub-sets of a given finite set</A>

in this site.



Also, &nbsp;you have this free of charge online textbook in ALGEBRA-I in this site

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson>ALGEBRA-I - YOUR ONLINE TEXTBOOK</A>.


The referred lessons are the part of this online textbook under the topic 
"<U>Miscellaneous word problems</U>".