Answer :

Given: P(n, 5) = 20 P(n, 3)


To find: value of n


We know,





So, according to question:


P(n, 5) = 20 P(n, 3)






(n – 3) (n – 4) = 20


n2 – 3n – 4n + 12 = 20


n2 – 7n + 12 – 20 = 0


n2 – 7n – 8 = 0


n2 – 8n + n – 8 = 0


n(n – 8) – 1(n – 8) = 0


(n – 8) (n – 1) = 0


n = 8 or 1


For, P(n, r): n ≥ r


n = 8 {for, P(n, 5)}


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