Q. 134.0( 8 Votes )

If P(15, r – 1) :

Answer :

Given: P(15, r – 1) : P(16, r – 2) = 3 : 4


To find: value of r


We know,





So, according to question:


P(15, r – 1) : P(16, r – 2) = 3 : 4








(18 – r) (17 – r) = 12


306 – 18r – 17r + r2 = 12


306 – 12 – 35r + r2 = 0


r2 – 35r + 294 = 0


r2 – 21r – 14r + 294 = 0


r(r – 21) – 14(r – 21) = 0


(r – 14) (r – 21) = 0


r = 14 or 21


For, P(n, r): r ≤ n


r = 14 {for, P(15, r – 1)}


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