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