The following problem is under the Bernoulli chapter in my book and it's about conditional convergence.

A hospital obtains its flu vaccines:

40% from A

50% from B

10% from C

Amount of ineffective vaccines:

3% in A

2% in B

5% in C

The hospital tests 5 vials from each shipment. If at least one of the five is ineffective, find the conditional probability of that shipment's having come from C.

I know how to solve the problem if the information in bold was not given. But I don't know how the information in bold changes the problem. Can any one explain ? How do I factor in them testing 5 vials.

thank you