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Answer :
(i) Numbers of defective bulbs = 4
The total numbers of bulbs = 20
\( P(E) \ = \ \frac{Number \ of \ favourable \ outcomes}{Total \ number \ of \ outcomes} \)
\(\therefore \) Probability of getting a defective bulb = P (defective bulb) \( = \ \frac{4}{20} \ = \ \frac{1}{5} \ = \ 0.2 \)
(ii) Since 1 non-defective bulb is drawn, then the total numbers of bulbs left are 19
So, the total numbers of events (or outcomes) = 19
Numbers of defective bulbs = 19 - 4 = 15
So, the probability that the bulb is not defective \( = \ \frac{15}{19} \ = \ 0.789 \)