J & K CET Engineering J and K - CET Engineering Solved Paper-2004

  • question_answer
    Seven digits from the digits 1, 2, 3, 4, 5, 6, 7, 8, 9 are written in a random order. The probability that these seven digit number is divisible by 9, is

    A)  \[\frac{2}{9}\]              

    B)  \[\frac{1}{5}\]

    C)  \[\frac{1}{3}\]               

    D)  \[\frac{1}{9}\]

    Correct Answer: D

    Solution :

    The number is divisible by 9, if the sum of the digits is divisible by 9. The seven digits number which is divisible by 9 are \[\{2,3,4,5,6,7,9\},\,\,\{1,3,4,5,6,8,9\}\] \[\{1,2,4,5,7,8,9\}\] and \[\{1,2,3,6,7,8,9\}\] \[\therefore \] Required probability \[=\frac{4\times 7!}{^{9}{{C}_{7}}\times 7!}=\frac{4}{\frac{9\times 8}{2\times 1}}\] \[=\frac{1}{9}\]


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