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If ""^(n)P(r) = 840 and ""^(n)C(r) = 35,...

If `""^(n)P_(r) = 840` and `""^(n)C_(r) = 35`, then r is equal to ………… .

Text Solution

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To solve the problem, we need to use the formulas for permutations and combinations. Given: - \( nP_r = 840 \) - \( nC_r = 35 \) We know the relationships between permutations and combinations: - \( nP_r = \frac{n!}{(n-r)!} \) ...
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Knowledge Check

  • If ""^(n)P_(r)=1680 and ""^(n)C_(r)=70 , then n is equal to

    A
    5
    B
    7
    C
    8
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    A
    6
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    7
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    8
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    10

  • If ""^(n)C_(r-1)=36,""^(n)C_(r)=84 and ""^(n)C_(r+1)=126 , then r is equal to

    A
    1
    B
    2
    C
    3
    D
    None of these

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