Librería Samer Atenea
Librería Aciertas (Toledo)
Kálamo Books
Librería Perelló (Valencia)
Librería Elías (Asturias)
Donde los libros
Librería Kolima (Madrid)
Librería Proteo (Málaga)
Learn several tricks to make doing hard addition problems much much easier. These tricks have been taught to elementry school children too! Everyone not only enjoys the simplicity, everyone also learns math on a deeper level. Many addition and subtraction problems become so much easier, that you can do them in your head without errors.