A box contains nine bulbs out of which 4 are defective. If four bulbs are chosen at random, find the probability that exactly three bulbs are good.

A. $$\frac{{20}}{{31}}$$

B. $$\frac{{20}}{{63}}$$

C. $$\frac{{5}}{{31}}$$

D. $$\frac{{6}}{{31}}$$

Answer: Option B

Solution(By Examveda Team)

Required probability
$$\eqalign{ & = \frac{{{}^5{C_3}\,.\,{}^4{C_1}}}{{{}^9{C_4}}} \cr & = \frac{{10 \times 4}}{{126}} \cr & = \frac{{20}}{{63}} \cr} $$