<PRE><B>Question 174555</B>
Let x = number of students enrolled in all three classes.  Since students are enrolled in at least two classes, there are four categories of students summarized below.  


x= Students in all three classes
170 -x = students in math and English but not history
150 - x = students in English and history but not math
300 - x = students in history and math but not English


The sum of these students must equal 500.

x + 170-x + 150-x + 300-x  = 500
620-2x = 500
-2x = -120
x=60 


R^2</PRE>