Răspuns :
a+b=21
a:b=4 rest 1
a=b×4+1
b×4+1+b=21
5b=20
b=20:5
b=4
a=21-4; a=17
verificare: 17+4=21 (A)
a+b=21
a:b=4rest1
a=4b+1
4b+1+b=21
5b=21-1
5b=20
b=20:5
b=4
a+4=21
a=21-4
a=17
a+b=21
a:b=4 rest 1
a=b×4+1
b×4+1+b=21
5b=20
b=20:5
b=4
a=21-4; a=17
verificare: 17+4=21 (A)
a+b=21
a:b=4rest1
a=4b+1
4b+1+b=21
5b=21-1
5b=20
b=20:5
b=4
a+4=21
a=21-4
a=17