MP90
Problem for November 2009

Consider a 4 by 4 grid of squares to be viewed as a crossword puzzle with four words across and four words down. In alphabetical order, seven of the eight words are

MPMM, OMPM, OMPP, OOMO, OOMP, POOM, and POPM.

What is the eighth word?

November's problem comes from the collection of Joe Konhauser (1924-1992), a long-time Mathematics professor at Macalester College.

Please note that in a solution to any math problem the explanation is all-important — every claim must be supported by some mathematical truth. 

Instructions for sending us your solution:

Please ensure that your solution contains your name and email or street address.

Solvers who submit their solutions by the 21^st of the month will have their names listed on the solutions page along with the best of the submitted solutions.

Solutions can be sent to us in three ways:

by email:	You must ensure that you start your subject line with [MP] otherwise our spam filter will delete your message. Send us your solution at .
or
by fax:	+1 (306) 585-4056 Mark it: Attention: Math Central
or
by post:	Math Central Student Development Centre University of Regina Regina, Saskatchewan S4S 0A2 Canada