Suppose the bulb drawn in (i) is not defective and not replaced. Now, bulb is drawn at random from the rest. What is the probability that this bulb is not defective?
Total numbers of elementary events are: 20 – 1 = 19
Let E be the event of getting not defective bulb and not replacing the bulb already drawn
The favourable outcomes = 19 - 4 = 15
∴ P (not defective bulb drawn after not replacing the already drawn bulb) = P (E) = 15/19