Answer:
3/5
Step-by-step explanation:
Remember that odds for plus odds against must be 1. Therefore, 20 out of 50 of the DVRs are defective, so 30 out of 50 would work.
30/50
simplifies into 3/5 so that would be the probability of you picking out a DVR that works, and the probability of picking one that does not work would be the leftover 2/5 . Or, if you're answering with a percent, you would have a 60% chance of picking a working DVR.
I hope this helps, I know the explanation isn't really clear, but I can't really think of another way to explain it.
