Mathematics - Permutation & Combination Question with Solution | TestHub

MathematicsPermutation & CombinationnPr & nCrEasy2 minPYQ_2024

MathematicsEasysingle choice

If $^{22} P_{r + 1} :^{20} P_{r + 2} = 11 : 52$ , then $r$ is equal to

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Solution:

$^{22} P_{r + 1} :^{20} P_{r + 2} = 11 : 52$ or $(21 - r) (20 - r) (19 - r) = 52 \times 2 \times 21$ $\Rightarrow (21 - r) (20 - r) (19 - r) = 14 \times 13 \times 12$ $\Rightarrow (21 - r) (20 - r) (19 - r) = (21 - 7) (20 - 7) (19 - 7)$ $\Rightarrow r = 7$

Stream:BITSATSubject:MathematicsTopic:Permutation & CombinationSubtopic:nPr & nCr

⏱ 2mℹ️ Source: PYQ_2024

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