MathDB

2

Part of 2012 Silk Road

Problems(1)

table 4x4, lines labeled 1,2,3,4, columns labeled a,b,c,d, written inside 0 or 1

Source: SRMC 2012

9/3/2018
In each cell of the table 4×44 \times 4, in which the lines are labeled with numbers 1,2,3,41,2,3,4, and columns with letters a,b,c,da,b,c,d, one number is written: 00 or 11 . Such a table is called valid if there are exactly two units in each of its rows and in each column. Determine the number of valid tables.
numbers in a tabletablecombinatorics