Expected values

Mock question
31. A battery manufacturer, who produces 500,000 units per month, inspects 10% of all units produced. Of those inspected it was found that 1% are faulty. Of the batteries which are not inspected there is 5% chance that a unit may be faulty. What is the probability to one decimal place that a faulty battery was actually inspected?

I have got no brains to answer this! How this is even a expected value question? ACCA is trying to mess with my head.