diff --git "a/Retos/Reto #28 - EXPRESI\303\223N MATEM\303\201TICA [Media]/python/marcoatrs.py" "b/Retos/Reto #28 - EXPRESI\303\223N MATEM\303\201TICA [Media]/python/marcoatrs.py"
new file mode 100644
index 0000000000..4a76461952
--- /dev/null
+++ "b/Retos/Reto #28 - EXPRESI\303\223N MATEM\303\201TICA [Media]/python/marcoatrs.py"	
@@ -0,0 +1,19 @@
+signos_permitidos = "0123456789+-/*% "
+parejas_invalidas = ["*/", "/*", "%/", "/%", "*%", "%*", "%%", "+/", "-/"]
+
+
+def expresion_matematica(expresion: str) -> bool:
+    # Caracter invalido
+    for c in expresion:
+        if c not in signos_permitidos:
+            return False
+    # Signos dobles
+    expresion = expresion.replace(" ", "")
+    for par in parejas_invalidas:
+        if par in expresion:
+            return False
+    return True
+
+print(expresion_matematica("2 + 4"))
+print(expresion_matematica("2 + /4"))
+print(expresion_matematica("2 +y 4"))