Question 1116679
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Let me re-tell the problem in this equivalent way:


<pre>
    Of 100 students, 40 failed in A;   30 failed in B;   25 failed in C;

                     15 failed in AB;  12 failed in BC;  10 failed in AC;

                      3 failed in ABC.

    How many students passed in all three papers ?
</pre>


<U>Solution</U>


<pre>
The number of those who failed at least in one of A, B and/or C is

    40 + 30 + 25 - 15 - 12 - 10 + 3 = 61.       (*)


The rest, 100-61 = 39 passed all three papers.


So,  {{{39/100}}}  of the class students,  or 39%, passed all three articles.
</pre>

Solved.


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If you want to know why and how the formula (*) works, the read these lessons

&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>

&nbsp;&nbsp;&nbsp;&nbsp;- <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.