1.

If 12P5 + 5. 12P4 = 13Pr , find r.

Answer»

We have (n–1)Pr + r. (n–1)P(r–1) = nPr and r ≤ n

12P5 + 5.12P4 = 13P5 = 13Pr (given) ⇒ r = 5



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