My sister has six red stamps and three blue ones. In her collection, seven stamps are from Mexico
and six stamps are from France. One stamp is purple and it is not from Mexico or France. Two
of her Mexican stamps are red and one is blue. Two of her French stamps are blue and three are red.
How many stamps does she have?
She has a minimum of 15 stamps.
Mexico: 1 blue, 2 red, 4 unknown color
France: 2 blue, 3 red, 1 unknown color
Unknown country: 1 purple, 1 red
... and for all we know, she might also have 2 green stamps from Germany.*