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14.Probability
easy
Dialing a telephone number an old man forgets the last two digits remembering only that these are different dialled at random. The probability that the number is dialled correctly, is
A
$\frac{1}{{45}}$
B
$\frac{1}{{90}}$
C
$\frac{1}{{100}}$
D
None of these
Solution
(b) There are $10$ digits $0,\,\,1,\,\,2,\,\,3,\,\,4,\,\,5,\,\,6,\,\,7,\,\,8,\,\,9.$
The last two digits can be dialled in ${}^{10}{P_2} = 90$ ways, out of which only one way is favourable,
thus the required probability $ = \frac{1}{{90}}.$
Standard 11
Mathematics
