Of 800 surveyed students, 20% of those who read book A also read book B and 25% of those who read book B also read book A. If each student read at least one of the books, what is the difference between the number of students who read only book A and the number of students who read only book B?  Choose the correct option: A) 20 B) 25 C) 30 D) 55 E) 100
Say the number of students who read book A is A and the number of students who read book B is B.   Given that 20% of those who read book A also read book B and 25% of those who read book B also read book A, so the number of students who read both books is 0.2A=0.25B --&gt; A=1.25B.   Since each student read at least one of the books then {total}={A}+{B}-{Both} --&gt; 800=1.25B+B-0.25B --&gt; B=400, A=1.25B=500 and {Both}=0.25B=100.   The number of students who read only book A is {A}-{Both}=500-100= 
<gadget id="calculator">500-100</gadget>
<output>400</output>
400;   The number of students who read only book B is {B}-{Both}=400-100= 
<gadget id="calculator">400-100</gadget>
<output>300</output>
300;   The difference is  400-300= 
<gadget id="calculator"> 400-300</gadget>
<output>100</output>
100.   Answer: 100.
<result>E</result>
Of 800 surveyed students, 20% of those who read book A also read book B and 25% of those who read book B also read book A. If each student read at least one of the books, what is the difference between the number of students who read only book A and the number of students who read only book B?