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Solution to Question 3.
For question 3, I found it helpful to keep track of wins and losses of each in a table then to list all 15 matches. Using each of the conditions, we can establish a lot; such as A and E must have 3 wins each as they cannot be 1 or 5. Similarly we work out the two with 1 win each and use this to determine the winner of each match and the undefeated winner.
Table of wins and losses
A 3-2
B 2-3
C 1-4
D 1-4
E 3-2
F 5-0
Winners of each match
AB A
AC A
AD A
AE E
AF F
BC B
BD D
BE B
BF F
CD C
CE E
CF F
DE E
DF F
EF F