A is the groupe of student with a Cd player.
B is the groupe of student with a telephone.
C is the groupe with a computer.
|A| = 700 = Card A
|B| = 850 = Card B
|C| = 452 = Card C
you looking for |A and B and C|
I would start finding |A and B| (the minimum of this is 550.) To find 550 here is what I did
|Non A| = 1000-700 = 300.
|B| -|Non A| = 550
You do the same thing with |(A and B) and C| the minimum value of this, if I didn't mess up. is 2.
Hope that helped!?