Twenty tickets are marked numbers 1, 2, ..... 20. If three tickets be drawn at random, then probabil

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14.Probability

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Twenty tickets are marked the numbers $1, 2, ..... 20.$ If three tickets be drawn at random, then what is the probability that those marked $7$ and $11$ are among them

A

$\frac{3}{{190}}$

B

$\frac{1}{{19}}$

C

$\frac{1}{{190}}$

D

None of these

Solution

(a) $7,\,\,11$ have always to be in that group of three,

therefore $3^{rd}$ ticket may be chosen in $18$ ways.

Hence required probability is $\frac{{18}}{{{}^{20}{C_3}}} = \frac{{18\,.\,3\,.\,2}}{{20\,.\,19\,.\,18}} = \frac{3}{{190}}$.

Standard 11

Mathematics

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