The problem is:
In carrying out a survey of the efficiency of the lights, brakes and steering of motor vehicles, 100 vehicles were found defective as follows:
35 defective lights
40 had defective brakes
41 had defective steering
8 had defective lights and brakes
7 had defective lights and steering
6 had defective brakes and steering
a) how many had defective lights, brakes and steering?
b) how many vehicles had defective lights only?
Now I know the answers are 5 and 25 respectively but I cannot form the correct equation to arrive at them.
I think the equation has to be in the form of
x(A u B u C)= x(A) + x(B) + x(C) - x(A n B) - x(A n C) - x(B n C) + (A n B n C)
I would appeciate help with the formulae.