MHB What is the Correct Value of r if 9!/(9-r)! = 840?

[mathdad]

9!/(9 - r)! = 840

I found r to be 4.

Is this correct?

 

[skeeter]

9!/(9 - r)! = 840

I found r to be 4.

Is this correct?

$\dfrac{9!}{(9-4)!} = \dfrac{9!}{5!} = 9 \cdot 8 \cdot 7 \cdot 6 = 3024$

there is no solution to the equation $\dfrac{9!}{(9-r)!} = 840$ for $0 \le r \le 9 \, , \, r \in \mathbb{Z}$

 

[mathdad]

I messed up in my calculation. Thanks.