Question 1012931
16 passed the first and four failed both. That is 
20 out of 30, leaving 10 who failed the first and 
passed the second.  Of 20 who passed the second, 
10 had failed the first, leaving 10 who passed both.
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So 4 failed both, 10 failed the first and passed the 
second, 6 passed the first and failed the second, and
10 passed both. Total: 30
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Four failed both, ten passed both, and 16 passed one 
of two. Total: 30.
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ANSWER: Ten students passed both tests.
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