posted by Kassie on .
A class has 50 students. 13 are juniors, 20 are psych majors, and 24 are neither psych majors nor juniors. How many psych majors are juniors?
Draw your Venn Diagram
My drawing shows that
Pr(Junior or Psy)= Pr(Jun)+ Pr(Psy)-Pr(Junior AND Psy)
But you are given Pr (NOT(Junior Or Psy), so Pr(Junior or Psy)=1-Pr( Not(junior or Psy).
Pr(Junior ANd Psy)=Pr(Jun)+Pr(Psy)-Pr(Jun or Psy)
= Pr(Jun)+ Pr(Psy)-(1-Pr(NOT(Jun or Psy))
= 13/50 + 20/50-1+24/50
so 7 Psy majors are Juniors.
check my thinking.
This is not physics. Please don't misrepresent your subject again.