Question

Find r if 5P(4,r) = 6P(5,r-1)​

Answer 1

$5 \times \frac{4!}{(4 - r)!} = 6 \times \frac{5!}{(6 - r)!} \\ \frac{5!}{(4 - r)!} = \frac{6 \times 5!}{(6 - r)(5 - r)(4 - r)!} \\ (6 - r)(5 - r) = 6 \\ (6 - r)(5 - r) = 3 \times 2 \\ 6 - r = 3 \\ r = 3$

Answer 2

Answer:

r = 3

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