Permutation & Combination

Firstly, the Permutation of the 3 parcels delivered to 3 places in the same district successively is 3! and that of the 4 parcels is 4!

Now we can see the 3 parcels as a whole and the 4 parcels as a whole, then there seem to be 7 parcels

the permutation of 7 parcels is 7!

then the no. of the delivery sequences is 7! x 4! x 3!

=7257560


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