Răspuns :
a + b = 999
a - b = 1
a = b + 1
b + 1 + b = 999
2b + 1 = 999
2b = 999 - 1
2b = 998
b = 998 : 2
b = 499
a - 499 = 1
a = 499 + 1
a = 500
a - b = 1
a = b + 1
b + 1 + b = 999
2b + 1 = 999
2b = 999 - 1
2b = 998
b = 998 : 2
b = 499
a - 499 = 1
a = 499 + 1
a = 500