Question

If a courier guy has to deliver 9 parcels in the same area in a day, in how many possible ways can he deliver them?

Answer 1

Let $n=9$ parcels.

For the $1^{st}$ parcel, the courier guy has 9 options to deliver it.

For the $2^{nd}$ parcel, the courier guy has 8 options to deliver it.

For the $3^{rd}$ parcel, the courier guy has 7 options to deliver it.

This continues up to the $9^{th}$ parcel where the courier guy has 1 option to deliver it.

Therefore, the courier guy can deliver the parcels in $n!=9!=362,880$ ways.