In: Statistics and Probability
A company has two machines that produce widgets. The new machine produces 75% widgets and the older machine produces 25% widgets. Further, the new machine produces 10% defective widgets, while the older machine produces 30% defective widgets. If a widget is randomly selected what is the probability that it is defective?
A company has two machines that produce widgets. The new machine produces 75% widgets and the old one produces 25% widgets.
The new machine produces 10% defective widgets, and the old machine produces 30% defective widgets.
So, given that
P(A randomly selected widget is produced by new machine)=75/100=0.75
P(A randomly selected widget is produced by old machine)=25/100=0.25
P(widget is defective|produced by new machine)=10/100=0.10
P(widget is defective|produced by old machine)=30/100=0.30
To find the chance that a randomly slected machine is defective.
So, we have to find
P(A randomly selcted machine is defective)
=P(A machine is defective and produced by old machine)+P(A machine is defective and produced by new machine)
From conditional probability, we know that P(A and B)=P(A)P(B|A).
Now, by total probability theorem, this becomes
=[P(widget is produced by new machine)*P(widget is defective|produced by new machine)]+[P(widget is produced by old machine)*P(widget is defective|produced by old machine)]
=0.75*0.10+0.25*0.30
=0.075+0.075
=0.150.
So, the probability that a randomly selected machine is defective is 0.150.