If ""nPr=840 and ""^nCr=35, then r is eq...

If `""_nP_r=`840 and `""^nC_r=35`, then r is equal to....

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KUMAR PRAKASHAN-PERMUTATIONS AND COMBINATIONS-PRACTICE WORK

Find r : ""^(5) P(r) =42 ""^(6)P(r-1)
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Prove that , ""^nPr = ""^((n-1))Pr + r. ""^(n-1)P((r-1))
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If ""nPr=840 and ""^nCr=35, then r is equal to....
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If ""^((n+2)) C8 :"" ^((n-2)) P4= 57 : 16 then find n.
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If ""^nC10= ""^nC12 then find ""^23Cn.
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