Tiling a chessboard with 1x3 triominos and T-tetrominos
Source: XII Rioplatense Mathematical Olympiad (2003), Level 3
August 8, 2011
geometryrectanglesymmetrygeometric transformationreflectionrotationcombinatorics unsolved
Problem Statement
An chessboard is to be tiled (i.e., completely covered without overlapping) with pieces of the following shapes:
[asy]
unitsize(.6cm);
draw(unitsquare,linewidth(1));
draw(shift(1,0)*unitsquare,linewidth(1));
draw(shift(2,0)*unitsquare,linewidth(1));
label("\footnotesize rectangle",(1.5,0),S);
draw(shift(8,1)*unitsquare,linewidth(1));
draw(shift(9,1)*unitsquare,linewidth(1));
draw(shift(10,1)*unitsquare,linewidth(1));
draw(shift(9,0)*unitsquare,linewidth(1));
label("\footnotesize T-shaped tetromino",(9.5,0),S);
[/asy] The rectangle covers exactly three squares of the chessboard, and the T-shaped tetromino covers exactly four squares of the chessboard. (a) What is the maximum number of pieces that can be used?
(b) How many ways are there to tile the chessboard using this maximum number of pieces?