Question

SI C.A. (abcd) = xxx
calcular x si sabe que:
a + b +c + d = 21

Answer 1

$CA(\overline{abcd})=\overline{xxx}\\ \\ 10000-\overline{abcd}=\overline{xxx}\\ \\ 10000-\overline{xxx}=\overline{abcd}\\ \\ \overline{xxx}\in\{111,222,\hdots,999\}\\ \\ \overline{abcd}\in\{8889,7778,6667,5556,\hdots,9001\}\\ \\ \to \overline{abcd}=5556\to \overline{xxx}=444\to \boxed{x=4}$