In a group of 68 students, each student is registered for at least one of three classes – History, Math and English. Twenty-one students are registered for History, twenty-six students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?	Pick one
A) 13 B) 10 C) 9 D) 8 E) 7
A U B U C = A + B + C - AB-BC-AC + ABC   68 = 21 + 26+ 34 -AB-BC-AC +3 =&gt; AB+BC+AC = 16   7xactly Two classes = AB+BC+AC - 3ABC = 16 -3*3= 
<gadget id="calculator">16 -3*3</gadget>
<output>7</output>
7   Hence 7
<result>E</result>
In a group of 68 students, each student is registered for at least one of three classes – History, Math and English. Twenty-one students are registered for History, twenty-six students are registered for Math, and thirty-four students are registered for English. If only three students are registered for all three classes, how many students are registered for exactly two classes?