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14.Probability
easy
A bag contains $6$ white, $7$ red and $5$ black balls. If $3$ balls are drawn from the bag at random, then the probability that all of them are white is
A
$\frac{{20}}{{204}}$
B
$\frac{5}{{204}}$
C
$\frac{1}{3}$
D
None of these
Solution
(b) $3$ ball can be drawn in ${}^{18}{C_3}$ ways
Favourable cases $ = {}^6{C_3}$
$\therefore $ Required probability $ = \frac{{{}^6{C_3}}}{{{}^{18}{C_3}}} $
$= \frac{{6 \times 5 \times 4}}{{18 \times 17 \times 16}} = \frac{5}{{204}}$.
Standard 11
Mathematics