Question

Problem :

It is reported that 50% of all computer chips produced are defective. Inspection ensures that only 5% of the chips legally marketed are defective. Unfortunately, some chips are stolen before inspection. If 1% of all chips on the market are stolen, find the probability that a given chip is stolen before it is defective.

Question :
In the solution I found, the events are defined like this.
A : Observing the chip is stolen.
B : Observing the chip is defective.

From the given information, there is 1% of all chips on the market are stolen.
That is, P(A) = 0.01. Also, 50% of all computer chips produced were defective.
That is, P(B|A) = 0.50 and 5% of the defective chips are legally marketed. That is, P(B|A`) = 0.05.
...

My question :

How does 50% of all computer chips produced were defective translate into P(B|A)?
Why is it not P(B)?

Answer 1