Which values of P and Q result in an equation with no solutions?
Px+40=Qx+20
Px + 40 = Qx + 20
Px +20 = Qx
20 = Qx - Px = (Q-P)x
If Q=P then (Q-P)x = 0 for all x and thus the original equation has no solutions.
+11 
