Dear student 10Pr=720⇒10!10-r!=10×72⇒10!10-r!=10×9×8⇒10!10-r!=10×9×8×7!7!⇒10!10-r!=10!7!⇒10-r!=7!⇒10-r=7⇒r=3 Regards

Find r if ¹⁰P_r = 720.

Dear student

^{10} P_{r} = 720 \Rightarrow \frac{10!}{(10 - r)!} = 10 \times 72 \Rightarrow \frac{10!}{(10 - r)!} = 10 \times 9 \times 8 \Rightarrow \frac{10!}{(10 - r)!} = \frac{10 \times 9 \times 8 \times 7!}{7!} \Rightarrow \frac{10!}{(10 - r)!} = \frac{10!}{7!} \Rightarrow (10 - r)! = 7! \Rightarrow 10 - r = 7 \Rightarrow r = 3

Regards

Find r if 10Pr = 720.