Three children: Alberto, Benito and Carlos wear shoes of different colors. Alberto's shoes are green, Benito's are blue and Carlos's are red. As we are in carnival, they decide to exchange their shoes with each other so that each one will have two shoes of two colors that are not their own.
Benito approaches me and shows me the red shoe of his right foot.
What color is Alberto's shoe on his right foot?
Since we know that nobody wears their own shoes, we deduce that the color of Benito's left shoe must be green. This means that Carlos has to wear the other green shoe on his right foot and therefore the blue one on his left foot.
Alberto's left foot shoe should be red and the one on the right blue foot.