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$$\eqalign{ & = \frac{{{}^5{C_3}\,.\,{}^4{C_1}}}{{{}^9{C_4}}} \cr & = \frac{{10 \times 4}}{{126}} \cr & = \frac{{20}}{{63}} \cr} $$
This Question Belongs to Arithmetic Ability >> Probability
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