Question

P(10,r)=2P(9,r),r is equal to - (a) 2 (b) 4 (c) 5 (d) 6

Answer 1

Answer:

no no answer

Step-by-step explanation:

no no explanation

Answer 2

Answer:

The value of r is equal to (c) 5.

Step-by-step explanation:

Given:

P(10, r) = 2P(9, r)

To find:

r =?

Formula:

$_nP_r = \frac{n!}{(n-r)!}$

Solution:

P(10, r) = 2P(9, r)

Therefore,

$\frac{10!}{(10-r)!} = 2 \frac{9!}{(9-r)!}$

$\frac{10!}{9!} = 2\frac{(10-r)!}{(9-r)!}$

$\frac{10*9!}{9!} = 2\frac{(10-r)(10-r-1)!}{(9-r)!}$

$\frac{10*9!}{9!} = 2\frac{(10-r)(9-r)!}{(9-r)!}$

10 = 2(10-r)

10 = 20 - 2r

2r = 20 - 10

2r = 10

r = 5

Therefore, the value of r is 5.

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