<p>You have 6 radios with 2 of them bad.
You draw 1 radio, and it is good.
So now there are 5 radios with 2 of them bad. Therefore, 3 of them are good.
The probability of drawing a good radio next = the number of good/ total radios left
3 good radios/ 5 total radios = 3/5</p>