Răspuns:
Explicație pas cu pas:
a+b=c+d=b+c+1=21, b+c = 21-1 =20
a+10b+11c+2d la a+d =
a+b +9b +9c +2c +2d =
a+b +9(b+c) +2(c+d) =
21 + 9*20 +2*21 =
21 +180 +42 = 63+180 = 243
Aflam a+d:
a+b =21
c+d = 21
Le adunam:
a+b +c+d = 21+21
a+d +b+c =42
a+d +20 =42
a+d = 42-20 =22
243 : 22 = 22*11 + 1
Rest = 1