Casey W. answered 06/15/15
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Mathematics (and Science) Instruction by a Mathematician!
The idea here is design an ALGORITHM, a process or collection of rules that an automaton could follow to sort mail.
Lets consider what the post office does...first mail needs to be delivered geographically, so lets first sort by ZIP CODE, then CITY.
Once that is sorted, we could sort the mail in each city (within a given zip code) by the street that the letter is being sent to...and lastly we can sort numerically by the number of the house on that street.
This would leave us with many piles of mail that are ready to be delivered by letter carriers, in numeric order of the houses along the street!.
An alternative approach, to perhaps facilitate delivery would be to first separate even and odd street addresses for each street prior to putting in numerical order. This would allow letter carriers (and their trucks with open doors and steering wheels on the opposite side of the vehicle) to simply drive down one side of the street delivering the (say even numbered) letters in order and then come back along the opposite side of the street delivering the other (odd numbered stack) in reverse order!
Hope this helps outline an algorithm that COULD be used to tell a machine how to sort mail for delivery purposes!