# Find r, if 5 <sup

5 4Pr = 6 5Pr-1     (6-r) (5-r) = 6

30 – 6r – 5r + r2 = 6

30 – 11r + r2 – 6 = 0

r2 –11r + 24 = 0

r2 –8r – 3r + 24 = 0

r(r-8)-3(r-8)=0

(r-8)(r-3)=0

r=8, r=3

As we know r<n,

So r<4,r<5.

r = 8 is not possible.

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