Question 1094776
<br>Any pen selected is from machine A or machine B or machine C; it can't be "from machines A & C", as your question asks.  So I don't know what you are really asking.<br>
Of each 1000 pens manufactured, 200 are from A, 300 from B, and 500 from C.  The defective pens are
5% of the 200 produced by A  (10);
3% of the 300 produced by B  (9); and
4% of the 500 produced by C  (20)<br>
There are a total of 39 defective pens.  If a defective pen is found, the probability is
10/39 that it was from A;
9/39 (=3/13) that it was from B; and
20/39 that it was from C.<br>
And to answer the question you actually asked, the probability is 0 that it came from A and C.