Fie a, b, c-numerele.
a+b+c=91
2a=c+7
b=c-10=>c=b+10
2a=b+10+7
2a=b+17
a=(b+17)/2
(b+17)/2+b+b+10=91
(b+17)/2+2b=91-10
(b+17)/2+2b=81 /*2
b+17+4b=162
5b=162-17
5b=145
b=145/5
b=29=>c=29+10=39
a=(29+17)/2=46/2=23
Verificare: 23+29+39=91 (adevărat)
Numerele căutate sunt: 23, 29, 39.