Răspuns :
a+c=718
b+d=523
a+b+c+d=?
a+c+b+d=
718+523=1241
a-b+c-d=X
a+b+c+d=1241
...............................
2a+2c=1241+X
2(a+c)=1241+X
2×718=1241+X
1436-1241=X
X=195
R:
a+b+c+d=1241
a-b+c-d=195
b+d=523
a+b+c+d=?
a+c+b+d=
718+523=1241
a-b+c-d=X
a+b+c+d=1241
...............................
2a+2c=1241+X
2(a+c)=1241+X
2×718=1241+X
1436-1241=X
X=195
R:
a+b+c+d=1241
a-b+c-d=195