Question

If nPr = 720 nCr, then r is equal to

Answer 1

Please see the attachment

Answer 2

r is equal to 6.

Step-by-step explanation:

Given : $^nP_r=720 ^nC_r$

To find : r is equal to ?

Solution :

We know that,

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

and $^nC_r=\frac{n!}{r!(n-r)!}$

Substituting,

$\frac{n!}{(n-r)!}=720(\frac{n!}{r!(n-r)!})$

$r!=720$

$r!=6\times 5\times 4\times 3\times 2\times 1$

$r!=6!$

$r=6$

Therefore, r is equal to 6.

#Learn more

Npr + r*npr-1 =n+1pr prove that.

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