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STD 11 - 14. probability — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsSTD 11 - 14. probability1 Mark
MCQ
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
    $\frac{1}{{45}}$
  • ✓
    $\frac{1}{{90}}$
  • C
    $\frac{1}{{100}}$
  • D
    None of these
✓

Answer

Correct option: B.
$\frac{1}{{90}}$
b
(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}}.$

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