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The total number of 4 digit numbers in which the digit are in descending order, isA. `""^(10)C_(4)xx4!`B. `""^(10)C_(4)`C. `(10!)/(4!)`D. none of these

Answer» The total number of arrangements of 10 digits 0, 1, 2,……,9 by taking 4 at a time `=""^(10)C_(4)xx4!`
We observe that in every arrangement in which the digits are in descending order. Hence,
The required number of numbers `=(""^(10)C_(4)xx4!)/(4!)=""^(10)C_(4)`.


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